diff --git a/devtools/client/shared/output-parser.js b/devtools/client/shared/output-parser.js
index 5202ae3a8e1e..76d6253ee643 100644
--- a/devtools/client/shared/output-parser.js
+++ b/devtools/client/shared/output-parser.js
@@ -21,7 +21,7 @@ const { LocalizationHelper } = require("resource://devtools/shared/l10n.js");
 const STYLE_INSPECTOR_L10N = new LocalizationHelper(STYLE_INSPECTOR_PROPERTIES);
 
 // Functions that accept an angle argument.
-const ANGLE_TAKING_FUNCTIONS = [
+const ANGLE_TAKING_FUNCTIONS = new Set([
   "linear-gradient",
   "-moz-linear-gradient",
   "repeating-linear-gradient",
@@ -37,17 +37,17 @@ const ANGLE_TAKING_FUNCTIONS = [
   "skewX",
   "skewY",
   "hue-rotate",
-];
+]);
 // All cubic-bezier CSS timing-function names.
-const BEZIER_KEYWORDS = [
+const BEZIER_KEYWORDS = new Set([
   "linear",
   "ease-in-out",
   "ease-in",
   "ease-out",
   "ease",
-];
+]);
 // Functions that accept a color argument.
-const COLOR_TAKING_FUNCTIONS = [
+const COLOR_TAKING_FUNCTIONS = new Set([
   "linear-gradient",
   "-moz-linear-gradient",
   "repeating-linear-gradient",
@@ -60,9 +60,14 @@ const COLOR_TAKING_FUNCTIONS = [
   "repeating-conic-gradient",
   "drop-shadow",
   "color-mix",
-];
+]);
 // Functions that accept a shape argument.
-const BASIC_SHAPE_FUNCTIONS = ["polygon", "circle", "ellipse", "inset"];
+const BASIC_SHAPE_FUNCTIONS = new Set([
+  "polygon",
+  "circle",
+  "ellipse",
+  "inset",
+]);
 
 const BACKDROP_FILTER_ENABLED = Services.prefs.getBoolPref(
   "layout.css.backdrop-filter.enabled"