I have Firefox 6.0 running on Vista. I have a sneaking suspicion that the subprogram that "clears the cache", et al., has a problem eliminating incomplete, erroneous, "currently in use", or "infinite loop" items, such that it freezes when trying to do so. After some experimentation, I found that the easiest way to resolve this is to do the following (it's easier than it looks): (1) Close all Firefox tabs and Firefox windows (2) Run the Task Manager and stop all "Firefox" processes (i.e., it's possible that more than one may be running, even if you did all of step (1)). (3) Go to the Firefox cache folder, usually located at <your system drive>\Users\<your personal named folder>\AppData*\Local\Mozilla\Firefox\Profiles\<something>.default\Cache, and wipe out everything that appears under that directory (n.b., you shouldn't require Administrative level clearance to do this; if so, try doing this in "Safe Mode"). ''{*AppData may be a "hidden" folder}'' (4) Run Firefox, then select Tools -> Options -> Advanced -> Network -> Clear Now. (5) Close Firefox. (6) Restart Firefox. Firefox ran considerably faster after I did this. Good luck!