After clicking the Clear Now button for the cache (Tools->Options->Offline Options->Clear Now) Firefox became unresponsive for several seconds until the cache was cleared. I had 123Mb in my cache. I expected that the cache would be cleared in the background and I could continue to use the browser. If not, at least I should get a progress dialog indicating that an action is taking place. Env: Thinkpad T42 WinXP Firefox 7.0.1

I just tested this on my Macbook Air and found the same behaviour. The browser becomes completely unresponsive while clearing the cache. In this case I had 1Gb in my cache. Env: Macbook Air OSX 10.7.2 Firefox 7.0.1

There was a problem in NTFS that was fixed long ago, and will be in Firefox 8. See bug 670911. Note it could hang your computer for minutes if you were using 1GB of cache. But that problem doesn't occur on Mac OS X. I'm not sure what you're seeing here, there really is a background thread used here the last couple of years. Maybe one of the bugs that bug 559729 depends on.

Given the work in bug 670911 I'm happy to resolve this bug as a dup. I can't reproduce the behaviour on OSX. I'll test again once I get my cache up to a significant size. If I encounter the problem I'll open another bug.