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:

• Firefox 4.0: http://www.mozilla.com/en-US/firefox/all.html

i have a English version, but at the time of instalation it goes to arabic.even i download a new one and still doing that.

Did you uninstall the Arabic version?
If you do then make sure not to remove personal data.

You can check the pref "general.useragent.locale" on the about:config and change the value of that pref to the name of the language version ("en-US" or "en-GB") if that still shows as "ar" 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.

You can update to Firefox 4.0.1 if you haven't done that yet via Firefox > Help > About Firefox

thanks for help,but i update came the same. and about the version i did what you said but everything is in Arabic and i don't understand it. i uninstall the Arabic version and kept my personal data.download a en-English version and install,still com the same.may be i have a bug or something in my computer

Did you check if there were leftover files in the Firefox program folder?

Do a clean (re-)install:

• Download a fresh Firefox copy and save the file to the desktop.
• Firefox 4.0: http://www.mozilla.com/en-US/firefox/all.html

• Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer.
• Do not remove personal data if you uninstall the current version.
• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere (not in the Firefox program folder) and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

Thanks again,I did what you said,still it come in Arabic.

Is the menu bar still in Arabic or do you mean other browser elements like bookmarks or web pages?

The menu bar should be in English if you install the English Firefox version.

Yes the menu bar still is in Arabic.there was no left over folder when i install it.