See Firefox takes a long time to start up and Firefox hangs or is not responding - How to fix for some ideas.

You could also go through Troubleshoot and diagnose Firefox problems, step by step.

Done, I do: - disabled some old and unused Add-ons & Plugins and, install the needed KB package, also set my Kaspersky to low and Firefox now acts more stable, for about 3 hours now... I'm keep testing in, but no problems for now, THANK YOU VEEEERY MUCH, THAT WAS VERY USEFUL!!!!

You're very welcome. Thanks for posting back.

Not sure what you meant by "also set my Kaspersky to low " but you might want to try changing that back to the default setting, if it affects your security, and see if Firefox remains stable. The other changes you made may have been enough to fix the problem.

I'll mark my answer above as solving your problem.

Yep, it, is still working, only one case of "Not Responding" but, It was my fault, so it doesn't Count! :D - The Kaspersky - I mean - Web Online protection scanner - the stuff that checks traffic in real time... It is already slowing down the machine... so the LOW state is fine for me... thus - I rarely checks unknown sites - only familiar ones :P

For your information:

http://kb.mozillazine.org/Error_loading_websites#Other_security_programs
Quote:
Note that some antivirus packages include web scanning features, such as AVG v9's "Link Scanner", Avast! "Web Shield" and Kaspersky "Web Anti-Virus", that process all HTTP traffic, which may cause intermittent timeouts and failed page loads (see below, under Websites randomly do not load) .
<snip>
Intermittent timeouts and failed page loads can be caused by web scanners bundled with certain anti-virus packages that process all HTTP traffic, such as Kaspersky "Web Anti-Virus" <snip> In such cases,

• In the Kaspersky "Web Anti-Virus" component, you can uncheck the "Scan HTTP traffic" option.