I have Persian Menu Bar and I wanted to change it to English, but it is almost impossible
My menu Bar is native (persian) language, I wanted to change it to English Menu Bar, it seems to be impossible
ప్రత్యుత్తరాలన్నీ (1)
If you have the Firefox user interface (menu bar) in the wrong language or want to change the current language then you can get Firefox in the language of your choice here:
Uninstall the current Firefox version, but make sure that you do not remove your personal data. Install the new Firefox version of the wanted language.
See also http://kb.mozillazine.org/Profile_backup and Back up and restore information in Firefox profiles
You may need to (re)set the pref "general.useragent.locale" to the preferred language (e.g. "en-US" or "en-GB") on the about:config page.
You can open the about:config page via the location bar, like you open a web site.
Use the Filter bar at the top of that page to quickly locate the pref.