If you want to change the language of your firefox, uninstall the current one on your pc, then visit this site and download the english version: http://www.mozilla.org/en-US/firefox/all.html

Whereas, on this site you can download language packs & dictionaries: https://addons.mozilla.org/en-US/firefox/language-tools/

Regards, G-Cloud.

if i uninstall firefox will i lose all my addons and personas and other stuff

Well, when you uninstall firefox it asks you if you want to delete also your settings, but I'm not sure if your add-ons will be deleted. You can try, instead, to install the language pack without deleting something.

i tried but i can only install a dictionary pack the language pack isn't avadible

Ok, try to install this: https://addons.mozilla.org/en-US/firefox/addon/quick-locale-switcher/

It should allow you to change the language.

solved i downloaded the english setup closed firefox and followd the instalation it found my previous version and updated it and i still have all my addons and themes and stuff thanks for your help

Perfect, it was a pleasure to help you. =)