I am using 10.5.5 (the latest update) and Firefox 3.01 (the latest version I assume) and often multi task several applications, including iTunes and Mail. Recently my system has locked in beach ball stage, Force Quit is very slow to respond and states that my open applications are not responding to the Force Quit function. This forces a reboot via the on/off button on my PowerBook G4. In past years I have very seldom had to force quit and/or reboot this computer. I have rebuilt my hard drives with Disk Utilities.
Any other ideas?
Probably an update-related problem. I would start by resetting the browsers and deleting their caches, then download and re-apply QuickTime 7.5.5, iTunes 8 and download and apply the (enormous) OS 10.5.5 combined update. After each update, repair disk permisssions.
Colin