Fix for RangeError: invalid language tag and client-side exceptions in Firefox on Linux
Hi everyone,
I was experiencing persistent JavaScript errors in Firefox on Linux … (read more)
Fix for RangeError: invalid language tag and client-side exceptions in Firefox on Linux
Hi everyone,
I was experiencing persistent JavaScript errors in Firefox on Linux when loading certain modern websites (e.g., built with React or Next.js). The browser console showed messages like:
RangeError: invalid language tag: "chrome://global/locale/intl.properties"
A client-side exception has occurred (see the browser console for more information)
React error #418 with minified stack traces
This happened even in Safe Mode, with all extensions disabled, cookies/cache cleared, and Enhanced Tracking Protection off.
✅ Root cause and fix:
Turns out the issue was related to missing or broken locale configuration in Firefox. To fix it:
Open about:config
Create a new string entry:
Name: intl.locale.requested
Value: en-US (or fr, en-GB, etc. — any valid locale)
Restart Firefox
After adding this key, all affected pages started working correctly. The invalid "chrome://global/locale/intl.properties" error in intl.accept_languages disappeared as well — it seems that was just a side effect of the missing locale setting.
🔁 Summary:
If you’re seeing RangeError: invalid language tag and React crashes, try adding intl.locale.requested manually. This fixed the issue entirely for me on Linux.
Hope this helps others!