This is usually caused by wither an extension, or anti-virus. What do you use for anti-virus on your machine (I've heard reports of webroot causing something like this).

You can try updating to Firefox 12, and if it still happens after that, Try to start Firefox in Safe mode. This mode disables all extensions, user customizations, hardware acceleration, etc. temporarily for diagnostic and troubleshooting. If Firefox works fine in Safe Mode, then this is likely an add-on issue. Restart Firefox in normal mode, then type "About:addons" (without the quotes) in the address bar. Disable your extensions one by one, restarting Firefox between each one, until you find the trouble maker.

and BTW, your English is great ;)

Try to use "Firefox/File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") to close Firefox if you are currently doing that by clicking the close X on the title bar.

See also:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

Sorry, don't work :[