diff --git a/src/components/middle/composer/hooks/useMentionTooltip.ts b/src/components/middle/composer/hooks/useMentionTooltip.ts
index 974814661..5ef53f7c1 100644
--- a/src/components/middle/composer/hooks/useMentionTooltip.ts
+++ b/src/components/middle/composer/hooks/useMentionTooltip.ts
@@ -15,7 +15,14 @@ const runThrottled = throttle((cb) => cb(), 500, true);
 const RE_BR = /(<br>|<br\s?\/>)/g;
 const RE_SPACE = /&nbsp;/g;
 const RE_CLEAN_HTML = /(<div>|<\/div>)/gi;
-const RE_USERNAME_SEARCH = new RegExp('(^|\\s)@[\\w\\d_-]*$', 'gi');
+let RE_USERNAME_SEARCH: RegExp;
+
+try {
+  RE_USERNAME_SEARCH = new RegExp('(^|\\s)@[-_\\p{L}\\p{M}\\p{N}]*$', 'gui');
+} catch (e) {
+  // Support for older versions of firefox
+  RE_USERNAME_SEARCH = new RegExp('(^|\\s)@[-_\\d\\wа-яё]*$', 'gi');
+}
 
 export default function useMentionTooltip(
   canSuggestMembers: boolean | undefined,
diff --git a/src/util/searchWords.ts b/src/util/searchWords.ts
index 5b3b52bd8..d423430a3 100644
--- a/src/util/searchWords.ts
+++ b/src/util/searchWords.ts
@@ -1,4 +1,11 @@
-const RE_NOT_LETTER = /[^\wа-яё]+/;
+let RE_NOT_LETTER: RegExp;
+
+try {
+  RE_NOT_LETTER = new RegExp('[^\\p{L}\\p{M}]+', 'ui');
+} catch (e) {
+  // Support for older versions of firefox
+  RE_NOT_LETTER = new RegExp('[^\\wа-яё]+', 'i');
+}
 
 export default function searchWords(haystack: string, needle: string) {
   if (!haystack || !needle) {