diff --git a/browser/components/urlbar/UrlbarInput.sys.mjs b/browser/components/urlbar/UrlbarInput.sys.mjs
index d9a04c782c2..4b69136aa31 100644
--- a/browser/components/urlbar/UrlbarInput.sys.mjs
+++ b/browser/components/urlbar/UrlbarInput.sys.mjs
@@ -5065,6 +5065,10 @@ function losslessDecodeURI(aURI) {
     }
   }
 
+  // IMPORTANT: The following regular expressions are Unicode-aware due to /v.
+  // Avoid matching high or low surrogate pairs directly, always work with
+  // full Unicode scalar values.
+
   // Encode potentially invisible characters:
   //   U+0000-001F: C0/C1 control characters
   //   U+007F-009F: commands
@@ -5083,7 +5087,7 @@ function losslessDecodeURI(aURI) {
   // preserve them encoded.
   value = value.replace(
     // eslint-disable-next-line no-control-regex
-    /[[\p{Separator}--\u0020]\p{Control}\u2800\ufffc]|\u0020(?=[\p{Other}\p{Separator}])|\s$/gv,
+    /[[\p{Separator}--\u{0020}]\p{Control}\u{2800}\u{FFFC}]|\u{0020}(?=[\p{Other}\p{Separator}])|\s$/gv,
     encodeURIComponent
   );
 
@@ -5094,21 +5098,18 @@ function losslessDecodeURI(aURI) {
   // per bug 582186:
   //   U+00AD, U+034F, U+06DD, U+070F, U+115F-1160, U+17B4, U+17B5, U+180B-180E,
   //   U+2060, U+FEFF, U+200B, U+2060-206F, U+3164, U+FE00-FE0F, U+FFA0,
-  //   U+FFF0-FFFB, U+1D173-1D17A (U+D834 + DD73-DD7A),
-  //   U+E0000-E0FFF (U+DB40-DB43 + U+DC00-DFFF)
+  //   U+FFF0-FFFB, U+1D173-1D17A, U+E0000-E0FFF
   // Bidi control characters (RFC 3987 sections 3.2 and 4.1 paragraph 6):
   //   U+061C, U+200E, U+200F, U+202A-202E, U+2066-2069
   // Other format characters in the Cf category that are unlikely to be rendered
   // usefully:
-  //   U+0600-0605, U+08E2, U+110BD (U+D804 + U+DCBD),
-  //   U+110CD (U+D804 + U+DCCD), U+13430-13438 (U+D80D + U+DC30-DC38),
-  //   U+1BCA0-1BCA3 (U+D82F + U+DCA0-DCA3)
+  //   U+0600-0605, U+08E2, U+110BD, U+110CD, U+13430-13438, U+1BCA0-1BCA3
   // Mimicking UI parts:
-  //   U+1F50F-1F513 (U+D83D + U+DD0F-DD13), U+1F6E1 (U+D83D + U+DEE1)
+  //   U+1F50F-1F513, U+1F6E1
   // Unassigned codepoints, sometimes shown as empty glyphs.
   value = value.replace(
     // eslint-disable-next-line no-misleading-character-class
-    /[\u00ad\u034f\u061c\u06dd\u070f\u115f\u1160\u17b4\u17b5\u180b-\u180e\u200b\u200e\u200f\u202a-\u202e\u2060-\u206f\u3164\u0600-\u0605\u08e2\ufe00-\ufe0f\ufeff\uffa0\ufff0-\ufffb\p{Unassigned}\p{Private_Use}]|\ud804[\udcbd\udccd]|\ud80d[\udc30-\udc38]|\ud82f[\udca0-\udca3]|\ud834[\udd73-\udd7a]|[\udb40-\udb43][\udc00-\udfff]|\ud83d[\udd0f-\udd13\udee1]/gv,
+    /[[\p{Format}--[\u{200C}\u{200D}]]\u{034F}\u{115F}\u{1160}\u{17B4}\u{17B5}\u{180B}-\u{180D}\u{3164}\u{FE00}-\u{FE0F}\u{FFA0}\u{FFF0}-\u{FFFB}\p{Unassigned}\p{Private_Use}\u{E0000}-\u{E0FFF}\u{1F50F}-\u{1F513}\u{1F6E1}]/gv,
     encodeURIComponent
   );
   return value;