Please do the following.

Press CTRL+SHIFT+DEL, change the setting at the top to Everything and then in the menu below, checkmark "Cache" (uncheck all the others). Then click the "Clear Now" button.

Next go to Tools | Options | Advanced | Network (tab) and in the Offline Storage menu, click the "Clear Now" button.

If it's a particular site which causes the problem, go to Tools | Options | Privacy and then click the "Show Cookies" button. Then delete all the cookies for that site.

Finally, go to File | Exit and then restart Firefox again.

If the problem persists in spite of the above troubleshooting steps, try running Firefox in Diagnose Firefox issues using Troubleshoot Mode. If it functions properly in that configuration, then one of your add-ons is the culprit.

If that doesn't help either, try creating a new Profile. See Profile Manager - Create, remove or switch Firefox profiles

Please read - 'When I try to clear my history, Firefox 4 crashes...'

CTRL+SHIFT+DELETE does what... It clears your history - stay with me here.

The problem is that Firefox 4 is crashing when an attempt is made to clear the history. Since all add-ons were disabled during the very recent install, I'm guessing its not that. Also, since I've tried this at my Google home page (after restarting Firefox and then my entire PC, I'm guessing its not the site being visited...

Anything else?

Try a fix from Firefox for the crashes??

Anyone?

PS. Attached, error message - unresponsive script. No... I dont use or have Chrome installed...

FYI - Deleting history in FF4 safe-mode works - even when selecting 'everything' and ticking all the boxes but this is definitely not an acceptable solution... PS (again) I have 1 plug-in enabled (shockwave flash) and 0 extensions. In FF3 I had 20 plug-ins and 13 extensions including the very same Shockwave flash...

Hopefully this info helps.

@ jenkotze, please see this article: Warning Unresponsive script - What it means and how to fix it

Incidentally, 'Chrome' is the Firefox control centre. It has nothing to do with Google Chrome. ;)

This can be caused by clearing the cookies via Delete browsing, search and download history on Firefox.

• Firefox/Tools > Options > Privacy > Firefox will: "Use custom settings for history" > [X] Clear history when Firefox closes > Settings
  

Try to exclude the cookies to see if that helps.
Let all cookies expire when you close Firefox to remove unwanted cookies and keep the ones with an allow exception.

• Tools > Options > Privacy > Cookies: "Keep until": "I close Firefox"

If you use Delete browsing, search and download history on Firefox to clear the cookies when you close Firefox then Firefox also tries to clear the cookies from plugins like Flash and starts a plugin-container process for each plugin and possibly for each cookie (?) and that can add extra time if there are a lot of cookies to remove and also can cause an unresponsive script error to appear.