Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

Thanks, but I doesn't change in safe mode

I have read here that many people have the same problem with this version of firefox.

It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.
Firefox stores session data every 10 seconds to make it possible to restore a crashed session.

Delete the files sessionstore.js [2] and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

If you see files sessionstore-##.js with a number in the left part of the name like sessionstore-1.js then delete those as well.
Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

See also:

• [1] http://kb.mozillazine.org/Session_Restore
• [2] http://kb.mozillazine.org/sessionstore.js

Thanks again, but it doesn't change. From time to time it appears: Mozilla no response

Firefox 5.0 doesn't work well . Try everything and always the same problem. I have no other way but try another product.