You can find all Firefox version here:

• http://www.mozilla.com/en-US/firefox/all-rc.html

Thanks for your help and for pointing me to a solution. However, this means a reinstallation of the browser in a different language. Isn't there a way to change the language setting after Firefox 4.0 has been installed?

You can install en-US language pack:

• http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0rc1/win32/xpi/

Set the pref "general.useragent.locale" to the name of the preferred language XPI file (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.

• http://kb.mozillazine.org/about%3Aconfig

Very helpful. Thanks!

You're welcome

I had the same problem! for me, the best solution is the following:

1) go to http://kb.mozillazine.org/Language_packs here you find an actual link to the language packs in any language, for firefox 4. They are in fact files called "xpi" (add-ons for firefox), to be found at http://releases.mozilla.org/pub/mozilla.org/firefox/releases/latest/win32/xpi/ (but this could change at a later point in time...).

2) click on the laguage pack you like (in the file list as above described), it will be installed immediately by firefox.

3) type about:config in your browser address bar, and go to "general.useragent.locale" (you can type this in the "filter" bar that you see there). Edit the value to the language shortcode you just downloaded, if this isn't done yet (eg: "en-GB" for british english, instead of "de-DE" for german!)

• Take care when editing the about:config file! This could damage your firefox installation.

• This solution takes just five minutes instead of 20-60 to download and reinstall Firefox in another language from scratch. Also, in case you have already other settings done, this could extend to several hours...

I use English and Spanish 50% - 50% Do I have to go through all that every 5 minutes??

You only need language packs if you need to change the language of the user interface.

• Locale Switcher: https://addons.mozilla.org/firefox/addon/356

If it is about spell checking then all you need to do is to install the dictionaries that you need.

You can look here for dictionaries:

• https://addons.mozilla.org/firefox/language-tools/

See also:

• http://kb.mozillazine.org/Spell_checking
• http://kb.mozillazine.org/Dictionaries
• https://support.mozilla.com/kb/Using+the+spell+checker

• Dictionary Switcher - https://addons.mozilla.org/firefox/addon/dictionary-switcher/
• Dafizilla Spell Check by Site: https://addons.mozilla.org/firefox/addon/dafizilla-spell-check-by-site/

I am using firefox 5 and the incredible amount of info i read on the subject was actually utterly useless and pointless.

I solved my firefox language woes by SIMPLY COPYING OVER THE OMNI.JAR file in the firefox directory.

- Installed the "other language" version in a different pc. - copied the "different version" omni.jar file over my version of firefox. - firefox now runs in english in my pc.