I've installed FF 3.6.3 on a multi-user system with the German language; however I'ld like to have everything in English (interface, etc.) for my user without installing a separate version of FF in English.
I've found the setting
general.useragent.locale and an extension, Quick locale switcher, but I don't actually understand where to get the locale from (en_US in my case, I guess).
I found pointers directing me to the official FTP release server with the hint to download the appropriate locale XPI, e.g. from http://releases.mozilla.org/pub/mozilla.org/firefox/releases/3.6.3/win32/en-US/ , however there's none.