diff --git a/build/build-clang/build-clang.py b/build/build-clang/build-clang.py
index 6daaa9e78af9..03521a333e78 100755
--- a/build/build-clang/build-clang.py
+++ b/build/build-clang/build-clang.py
@@ -446,7 +446,7 @@ def prune_final_dir_for_clang_tidy(final_dir, target):
         if is_darwin(target) and name in ["libLLVM.dylib", "libclang-cpp.dylib"]:
             continue
         if is_linux(target) and (
-            fnmatch.fnmatch(name, "libLLVM*.so*")
+            fnmatch.fnmatch(name, "libLLVM*.so")
             or fnmatch.fnmatch(name, "libclang-cpp.so*")
         ):
             continue
diff --git a/build/build-rust/cargo-vendor-std.patch b/build/build-rust/cargo-vendor-std.patch
index aa439d094b97..1a79846d6182 100644
--- a/build/build-rust/cargo-vendor-std.patch
+++ b/build/build-rust/cargo-vendor-std.patch
@@ -9,18 +9,18 @@ Most of these changes just add/edit tests for the functionality. Only the
 change to src/cargo/core/compiler/standard_lib.rs is important.
 
 diff --git a/src/cargo/core/compiler/standard_lib.rs b/src/cargo/core/compiler/standard_lib.rs
-index 9f96ca27d..80723c06b 100644
+index c456c58d5..333389bc8 100644
 --- a/src/cargo/core/compiler/standard_lib.rs
 +++ b/src/cargo/core/compiler/standard_lib.rs
 @@ -11,6 +11,7 @@ use crate::ops::{self, Packages};
  use crate::util::errors::CargoResult;
- use crate::GlobalContext;
+ use crate::Config;
  use std::collections::{HashMap, HashSet};
 +use std::fs;
  use std::path::PathBuf;
  
  use super::BuildConfig;
-@@ -73,27 +74,45 @@ pub fn resolve_std<'gctx>(
+@@ -73,27 +74,45 @@ pub fn resolve_std<'cfg>(
      }
  
      let src_path = detect_sysroot_src_path(target_data)?;
diff --git a/build/build-rust/rust-vendor-std.patch b/build/build-rust/rust-vendor-std.patch
index f72e64d8911f..e3ad25d1b012 100644
--- a/build/build-rust/rust-vendor-std.patch
+++ b/build/build-rust/rust-vendor-std.patch
@@ -11,12 +11,12 @@ their contents are ignored in favour of the actual stdlib.
 For firefox's purposes, these patches still work fine, and are necessary
 to make -Zbuild-std work in a vendored environment.
 
-diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
-index 012d64e5344..aedb53358ef 100644
+diff --git a/src/bootstrap/dist.rs b/src/bootstrap/dist.rs
+index 3cb0eccd324..a3b8154c024 100644
 --- a/src/bootstrap/src/core/build_steps/dist.rs
 +++ b/src/bootstrap/src/core/build_steps/dist.rs
-@@ -927,6 +927,31 @@ fn run(self, builder: &Builder<'_>) -> GeneratedTarball {
-             builder.copy_link(&builder.src.join(file), &dst_src.join(file));
+@@ -905,6 +905,31 @@ fn run(self, builder: &Builder<'_>) -> GeneratedTarball {
+             builder.copy(&builder.src.join(file), &dst_src.join(file));
          }
  
 +        // libsysroot includes std and everything else, so vendoring it
@@ -47,11 +47,11 @@ index 012d64e5344..aedb53358ef 100644
          tarball.generate()
      }
  }
-diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
-index 5ed6b357e20..ad617948c4b 100644
+diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
+index 3ed53452309..1fc0d887748 100644
 --- a/src/bootstrap/src/lib.rs
 +++ b/src/bootstrap/src/lib.rs
-@@ -1649,6 +1649,27 @@ fn read_stamp_file(&self, stamp: &Path) -> Vec<(PathBuf, DependencyType)> {
+@@ -1437,6 +1437,27 @@ fn read_stamp_file(&self, stamp: &Path) -> Vec<(PathBuf, DependencyType)> {
          paths
      }
  
@@ -61,7 +61,7 @@ index 5ed6b357e20..ad617948c4b 100644
 +        if self.config.dry_run() {
 +            return;
 +        }
-+        self.verbose_than(1, || println!("Copy {:?} to {:?}", src, dst));
++        self.verbose_than(1, &format!("Copy {:?} to {:?}", src, dst));
 +        if src == dst {
 +            return;
 +        }
@@ -76,6 +76,6 @@ index 5ed6b357e20..ad617948c4b 100644
 +        t!(filetime::set_file_times(dst, atime, mtime));
 +    }
 +
-     /// Links a file from `src` to `dst`.
-     /// Attempts to use hard links if possible, falling back to copying.
-     /// You can neither rely on this being a copy nor it being a link,
+     /// Copies a file from `src` to `dst`
+     pub fn copy(&self, src: &Path, dst: &Path) {
+         self.copy_internal(src, dst, false);
diff --git a/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp b/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp
index 5e09e093d083..36f981527249 100644
--- a/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp
+++ b/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp
@@ -199,12 +199,7 @@ public:
 #endif
                                   StringRef SearchPath,
                                   StringRef RelativePath,
-#if CLANG_VERSION_MAJOR >= 19
-                                  const Module *SuggestedModule,
-                                  bool ModuleImported,
-#else
                                   const Module *Imported,
-#endif
                                   SrcMgr::CharacteristicKind FileType) override;
 
   virtual void MacroDefined(const Token &Tok,
@@ -2348,12 +2343,7 @@ void PreprocessorHook::InclusionDirective(SourceLocation HashLoc,
 #endif
                                           StringRef SearchPath,
                                           StringRef RelativePath,
-#if CLANG_VERSION_MAJOR >= 19
-                                          const Module *SuggestedModule,
-                                          bool ModuleImported,
-#else
                                           const Module *Imported,
-#endif
                                           SrcMgr::CharacteristicKind FileType) {
 #if CLANG_VERSION_MAJOR >= 15
   if (!File) {
diff --git a/mozglue/static/rust/build.rs b/mozglue/static/rust/build.rs
index b3de7da6e4c3..1daa5840701b 100644
--- a/mozglue/static/rust/build.rs
+++ b/mozglue/static/rust/build.rs
@@ -16,10 +16,10 @@ fn main() {
     println!("cargo:rerun-if-changed=wrappers.cpp");
 
     let ver = version().unwrap();
-    let max_oom_hook_version = Version::parse("1.79.0-alpha").unwrap();
+    let max_oom_hook_version = Version::parse("1.78.0-alpha").unwrap();
     // The new alloc error panic feature was temporarily reverted. We kept the
     // code in tree, but the version here is such that it's effectively never used.
-    let max_alloc_error_panic_version = Version::parse("1.79.0-alpha").unwrap();
+    let max_alloc_error_panic_version = Version::parse("1.78.0-alpha").unwrap();
 
     if ver < max_oom_hook_version {
         println!("cargo:rustc-cfg=feature=\"oom_with_hook\"");
diff --git a/taskcluster/kinds/fetch/toolchains.yml b/taskcluster/kinds/fetch/toolchains.yml
index cbc3f7f88b3c..6b6045f7f56c 100644
--- a/taskcluster/kinds/fetch/toolchains.yml
+++ b/taskcluster/kinds/fetch/toolchains.yml
@@ -380,13 +380,13 @@ clang-trunk:
 # We build stable rust from source so the resulting compiler acts as a nightly
 # rust compiler, allowing to use unstable features like -Zbuild-std and
 # sanitizers.
-rust-1.78.0:
-    description: Rust 1.78.0 source code
+rust-1.77.2:
+    description: Rust 1.77.2 source code
     fetch:
         type: git
         include-dot-git: true
         repo: https://github.com/rust-lang/rust/
-        revision: 9b00956e56009bab2aa15d7bff10916599e3d6d6
+        revision: 25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04
 
 wasi-sdk-11:
     description: wasi-sdk-11 source code
diff --git a/taskcluster/kinds/toolchain/clang-tidy.yml b/taskcluster/kinds/toolchain/clang-tidy.yml
index 671e8f708192..02d089eca3d6 100644
--- a/taskcluster/kinds/toolchain/clang-tidy.yml
+++ b/taskcluster/kinds/toolchain/clang-tidy.yml
@@ -24,7 +24,7 @@ job-defaults:
             - 'build/build-clang/build-clang.py'
     fetches:
         fetch:
-            - clang-18
+            - clang-17
 
 linux64-clang-tidy:
     index:
@@ -39,7 +39,7 @@ linux64-clang-tidy:
             - 'build/build-clang/clang-tidy-linux64.json'
     fetches:
         toolchain:
-            - linux64-clang-18
+            - linux64-clang-17
             - linux64-toolchain-sysroot
 
 macosx64-clang-tidy:
@@ -58,7 +58,7 @@ macosx64-clang-tidy:
             - 'build/build-clang/macosx64.json'
     fetches:
         toolchain:
-            - linux64-clang-18
+            - linux64-clang-17
             - macosx64-sdk-toolchain
 
 macosx64-aarch64-clang-tidy:
@@ -79,7 +79,7 @@ macosx64-aarch64-clang-tidy:
             - 'build/build-clang/macosx64-aarch64.json'
     fetches:
         toolchain:
-            - linux64-clang-18
+            - linux64-clang-17
             - macosx64-sdk-toolchain
 
 win64-clang-tidy:
@@ -101,7 +101,7 @@ win64-clang-tidy:
             - 'build/build-clang/win64.json'
     fetches:
         toolchain:
-            - linux64-clang-18
+            - linux64-clang-17
             - vs-toolchain
             - win64-libxml2
 
@@ -124,5 +124,5 @@ linux64-clang-tidy-external:
         fetch:
             - civet-source
         toolchain:
-            - linux64-clang-18
+            - linux64-clang-17
             - linux64-toolchain-sysroot
diff --git a/taskcluster/kinds/toolchain/clang.yml b/taskcluster/kinds/toolchain/clang.yml
index 95d8b5c7e0f5..a9cf04e0b9b7 100644
--- a/taskcluster/kinds/toolchain/clang.yml
+++ b/taskcluster/kinds/toolchain/clang.yml
@@ -122,6 +122,10 @@ linux64-clang-17-mingw-x86:
             - 'x86'
         resources:
             - 'taskcluster/scripts/misc/mingw-*.patch'
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: linux64-clang-mingw-x86
         toolchain-artifact: public/build/clangmingw.tar.zst
     fetches:
         fetch:
@@ -144,6 +148,10 @@ linux64-clang-17-mingw-x64:
             - 'x64'
         resources:
             - 'taskcluster/scripts/misc/mingw-*.patch'
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: linux64-clang-mingw-x64
         toolchain-artifact: public/build/clangmingw.tar.zst
     fetches:
         fetch:
@@ -169,6 +177,10 @@ linux64-clang-17-stage1:
             - 'build/build-clang/linux64.json'
             - 'build/build-clang/clang-17.json'
             - 'build/build-clang/1stage.json'
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: linux64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         fetch:
@@ -238,6 +250,10 @@ linux64-clang-17:
         max-run-time: 600
     run:
         script: repack-clang.sh
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: linux64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -300,6 +316,12 @@ macosx64-clang-17:
         max-run-time: 600
     run:
         script: repack-clang.sh
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default:
+                    - macosx64-clang
+                    - macosx64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -364,6 +386,10 @@ macosx64-aarch64-clang-17:
         max-run-time: 600
     run:
         script: repack-clang.sh
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: macosx64-aarch64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -400,6 +426,10 @@ win64-clang-17-stage1:
             - 'build/build-clang/win64.json'
             - 'build/build-clang/clang-17.json'
             - 'build/build-clang/1stage.json'
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: win64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         fetch:
@@ -451,6 +481,10 @@ win64-clang-17:
         max-run-time: 600
     run:
         script: repack-clang.sh
+        toolchain-alias:
+            by-project:
+                toolchains: null
+                default: win64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -484,10 +518,6 @@ linux64-clang-18-mingw-x86:
             - 'x86'
         resources:
             - 'taskcluster/scripts/misc/mingw-*.patch'
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: linux64-clang-mingw-x86
         toolchain-artifact: public/build/clangmingw.tar.zst
     fetches:
         fetch:
@@ -510,10 +540,6 @@ linux64-clang-18-mingw-x64:
             - 'x64'
         resources:
             - 'taskcluster/scripts/misc/mingw-*.patch'
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: linux64-clang-mingw-x64
         toolchain-artifact: public/build/clangmingw.tar.zst
     fetches:
         fetch:
@@ -539,10 +565,6 @@ linux64-clang-18-stage1:
             - 'build/build-clang/linux64.json'
             - 'build/build-clang/clang-18.json'
             - 'build/build-clang/1stage.json'
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: linux64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         fetch:
@@ -612,10 +634,6 @@ linux64-clang-18:
         max-run-time: 600
     run:
         script: repack-clang.sh
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: linux64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -678,12 +696,6 @@ macosx64-clang-18:
         max-run-time: 600
     run:
         script: repack-clang.sh
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default:
-                    - macosx64-clang
-                    - macosx64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -748,10 +760,6 @@ macosx64-aarch64-clang-18:
         max-run-time: 600
     run:
         script: repack-clang.sh
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: macosx64-aarch64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
@@ -788,10 +796,6 @@ win64-clang-18-stage1:
             - 'build/build-clang/win64.json'
             - 'build/build-clang/clang-18.json'
             - 'build/build-clang/1stage.json'
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: win64-clang-toolchain
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         fetch:
@@ -843,10 +847,6 @@ win64-clang-18:
         max-run-time: 600
     run:
         script: repack-clang.sh
-        toolchain-alias:
-            by-project:
-                toolchains: null
-                default: win64-clang
         toolchain-artifact: public/build/clang.tar.zst
     fetches:
         toolchain:
diff --git a/taskcluster/kinds/toolchain/rust.yml b/taskcluster/kinds/toolchain/rust.yml
index 0e748d6eb0b1..e1e2778f68a4 100644
--- a/taskcluster/kinds/toolchain/rust.yml
+++ b/taskcluster/kinds/toolchain/rust.yml
@@ -26,12 +26,12 @@ linux64-rust-1.76:
             - linux64-rust-base
             - linux64-rust-toolchain
 
-linux64-rust-1.78:
+linux64-rust-1.77:
     treeherder:
         symbol: TL(rust)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'i686-unknown-linux-gnu',
@@ -62,18 +62,18 @@ linux64-rust-dev:
         ]
     fetches:
         fetch:
-            - rust-1.78.0
+            - rust-1.77.2
         toolchain:
             - linux64-clang-toolchain
             - linux64-toolchain-sysroot
 
-linux64-rust-cross-1.78:
+linux64-rust-cross-1.77:
     description: "rust repack with macos and windows cross support"
     treeherder:
         symbol: TL(rust-cross)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'i686-unknown-linux-gnu',
@@ -90,13 +90,13 @@ linux64-rust-cross-1.78:
         ]
         toolchain-alias: linux64-rust-cross
 
-linux64-rust-static-1.78:
+linux64-rust-static-1.77:
     description: "rust repack with static linking support"
     treeherder:
         symbol: TL(rust-static)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'aarch64-unknown-linux-musl',
             '--target', 'x86_64-unknown-linux-gnu',
@@ -120,13 +120,13 @@ linux64-rust-macos-1.70:
         ]
         toolchain-alias: linux64-rust-macos-toolchain
 
-linux64-rust-macos-1.78:
+linux64-rust-macos-1.77:
     description: "rust repack with macos-cross support"
     treeherder:
         symbol: TL(rust-macos)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-apple-darwin',
@@ -134,13 +134,13 @@ linux64-rust-macos-1.78:
         ]
         toolchain-alias: linux64-rust-macos
 
-linux64-rust-ios-1.78:
+linux64-rust-ios-1.77:
     description: "rust repack with ios-cross support"
     treeherder:
         symbol: TL(rust-ios)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'aarch64-apple-ios',
@@ -148,13 +148,13 @@ linux64-rust-ios-1.78:
         ]
         toolchain-alias: linux64-rust-ios
 
-linux64-rust-android-1.78:
+linux64-rust-android-1.77:
     description: "rust repack with android-cross support"
     treeherder:
         symbol: TL(rust-android)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'armv7-linux-androideabi',
@@ -179,13 +179,13 @@ linux64-rust-windows-1.70:
         ]
         toolchain-alias: linux64-rust-windows-toolchain
 
-linux64-rust-windows-1.78:
+linux64-rust-windows-1.77:
     description: "rust repack with windows-cross support"
     treeherder:
         symbol: TL(rust-win)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-unknown-linux-gnu',
             '--target', 'x86_64-pc-windows-msvc',
@@ -194,12 +194,12 @@ linux64-rust-windows-1.78:
         ]
         toolchain-alias: linux64-rust-windows
 
-win64-rust-1.78:
+win64-rust-1.77:
     treeherder:
         symbol: TW64(rust)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-pc-windows-msvc',
             '--target', 'x86_64-pc-windows-msvc',
             '--target', 'i686-pc-windows-msvc',
@@ -207,23 +207,23 @@ win64-rust-1.78:
         ]
         toolchain-alias: win64-rust
 
-macosx64-rust-1.78:
+macosx64-rust-1.77:
     treeherder:
         symbol: TM(rust)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-apple-darwin',
             '--target', 'x86_64-apple-darwin',
         ]
         toolchain-alias: macosx64-rust
 
-mingw32-rust-1.78:
+mingw32-rust-1.77:
     treeherder:
         symbol: TMW(rust)
     run:
         arguments: [
-            '--channel', '1.78.0',
+            '--channel', '1.77.2',
             '--host', 'x86_64-unknown-linux-gnu',
             '--target', 'i686-unknown-linux-gnu',
             '--target', 'i686-pc-windows-gnu',
diff --git a/tools/clang-tidy/config.yaml b/tools/clang-tidy/config.yaml
index 235947a03bce..773e92914faf 100644
--- a/tools/clang-tidy/config.yaml
+++ b/tools/clang-tidy/config.yaml
@@ -19,7 +19,7 @@ platforms:
 # Minimum clang-tidy version that is required for all the following checkers
 # to work properly.
 # This is also used by 'mach clang-format'
-package_version: "18.1.4"
+package_version: "17.0.6"
 clang_checkers:
   - name: -*
     publish: !!bool no