Try to only clear one item at the time via the details button in "Tools > Delete browsing, search and download history on Firefox" to see which choice is causing the freeze.

Mine eventually times out with:

'A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.'

Script: chrome://browser/content/sanitize.js:136

It never completes.

I have had this problem ever since updating to Firefox 4.0 running on Windows XP SP3. I found that the problem was with "cookies". If this was checked it would hang and I would get the script error message. Nothing I did would solve the problem till yesterday when I updated to the Firefox 5.0 beta and now the problem is solved. Whatever has changed in this beta release it solved the problem!

Hi.

Tried to respond to another post on this issue, but was informed that i did not have the right to do so...

In that post, Cor-el suggested the "elimination" method to establish which of the variety of things one wants to clear in browsing history causes the problem. Well I've done this on my own in the past, and it is TRUE. Clearing the history for cookies for any time range causes Firefox to freeze and a "script running" message will appear.

Cor-el suggested in that other post that due to Firefox requesting plugins to also delete cookie history that the program can hang...

Is there a way to delete cookie history for individual plugins (I only have three plugins so the process of elimination should work fairly quickly... I suspect that it might have something to do with the AdBlock plugin I'm using, since this problem started after I installed it) one at a time? That way I could establish what the issues is and inform the person who created the plugin to check out what the problem is... tho I also suspect (if it is the AdBlock plugin) those who create cookies to TRACK your online behavior will do what ever it takes to ensure you cannot delete those cookies... but then having been online for 22 years now may have just made me paranoid about these things?! :D

Please let me know if there is a solution!