Sam, I'm seeing the same thing. I've booted FF into safe mode, disabled all extensions and plug-ins, updated Windows and uninstalled and reinstalled FF multiple times, the last time removing all user data. However I still seeing FF peak at 99% CPU usage in both normal and safe mode and the memory usage continues to climb until FF just shuts down. It will be okay with one tab shortly after opening a second, it starts this behavior. I've checked to see if it submits a crash report but it does not. I feel like I've tried everything I find in the troubleshooting KB articles - I'll share if I find a solution but I'm spinning wheels at this point and considering trying to downgrade...or switch browsers.