I think I found the problem:

3 days ago I moved from Win XP to 7. I`ve backed up my Firefox profile with FEBE extension. On the XP i`ve used F-Secure IS 2011. Now on Win 7 I use F-Secure TP beta & I restored the FF profile but when I tried to start with this profile FF crashed! When I try to customize the FF buttons & toolbars FF crashes. I think the problem is F-Secures Browser Protection Toolbar. I`ve disabled this FF extension and the problem with customization is gone. Anyway I still can not start my previous restored profile. I think because of the different versions of the F-Secure BPT FF can not start this profile. It is so annoying!!! Can you make this conflict gone? May be FF automatically to disable the conflicted extension and not to crash!

Firefox does automatically disable extensions that aren't compatible with the version of Firefox that is being used.

Try disabling all your extensions while running on the Firefox SafeMode and then re-enable all but the extension that you are having problems with when back in the normal mode.
http://support.mozilla.com/en-US/kb/Safe+Mode

I know that but with disabled extensions I can not star the restored profile. No problem starting the default profile. Is there a way to disable extension from the backed up FEBE profile that I`m trying to restore???

You can disable extensions in your FEBE backup, but it is a little tricky and possibly error-prone. Inside your profile backup (profileFx3{profName}.fbu) there is a filed named "extensions.rdf". For each extension entry in that file, you can add the line NS1:userDisabled="true" after the "RDF:Description RDF:about="urn:mozilla:item:..." line.

You can use a utility like 7-zip to edit the file while keeping it in the archive (.fbu is just a renamed .zip file).

I`ve made everything you said but doesn`t work. When I restore this edited profile it starts BUT only with 2 extensions - this F-Secure BPT and Java Console. And my bookmarks aren`t in the profile. Something like new installation of FF. Can I delete something (the 4 extension.* files and the extension folder) in the backup to restore only bookmarks & themes. I can download the extensions again?

Did you follow all of the steps, in order, on the FEBE web site? I have used this procedure several times with no problems.
http://softwarebychuck.com/febe/tutorial/febeRestoreProfile.html

YES! I`ve used FEBE many many times without a problem .... until now.

You can remove extensions.* and the extensions folder from the backup, but you will lose any installed themes as well. You can always re-install them from AMO.

Your history and bookmarks are in the file named places.sqlite which you can extract from the full backup into your profile directory. In the future, you should consider doing a selective backup as well as the full profile backup. That way you can restore only the items you need.

Yes, I should backup bookmarks at least 2 times :)