diff --git a/browser/themes/shared/tabbrowser/content-area.css b/browser/themes/shared/tabbrowser/content-area.css
index be690ac92dc2..5fec50fdbccf 100644
--- a/browser/themes/shared/tabbrowser/content-area.css
+++ b/browser/themes/shared/tabbrowser/content-area.css
@@ -220,6 +220,13 @@
   padding: 0;
   overflow-x: auto;
 
+  /* Ensure that dialog boxes are pixel-snapped, to keep their internal layout
+   * consistent, regardless of whether the surrounding layout places them at a
+   * fractional position. (This helps prevent arbitrary 1px shifts that could
+   * otherwise appear inside of a vertically-centered dialog when the
+   * viewport-height changes from being odd to even.) */
+  will-change: transform;
+
   &:not(.spotlightBox) {
     box-shadow: 0 2px 14px 0 rgba(0, 0, 0, 0.2);
     border-radius: 8px;