and Firefox 4.0Beta12 don't seem to get along. That's how it looks like.
I tried numerous times to upload pictures in Photobucket and Adobe Flash would crash and my PC would freeze. Of course I had Adblock Plus and NoScript disabled in Firefox for Photobucket. I understand that Avast! may not support any (browser)Beta version.
Did some problem shooting and found out that uploading pics in IE8, Chrome and PaleMoon browsers went without a hitch.
Removed Flash, reinstalled, same problem. New version today of Flash also didn't solve it.
Then I removed Avast!'s SCRIPT FIELD, rebooted and after that the uploading of pics worked.

Just posted the above in case it may help someone with the very same problems.