I've been having the absolute worst Firefox experience in Kubuntu recently. I can't pinpoint the exact time that it started but it got a lot worse when I upgraded to Flash 10 (what a hog! Adobe seriously? Flash 10 runs about as well as a Microsoft OS does!).

Once Flash 10 was there scrolling in Firefox became impossible. It was as if my whole computer was locked for about 5 seconds. Then it would scroll... slowly. Painfully even.

After poking around in Google for a while and not finding much in the way of solutions, I decided to try some new video drivers. I uninstalled all of the Ubuntu Nvidia drivers and downloaded and installed the 177.80 drivers. 

Wow! What a huge difference. Not only that, but almost all of my issues with hibernation (it was intermittent, but sometimes it didn't work) are gone now too. 

One thing I did run into was that I didn't uninstall the Ubuntu Nvidia packages and just ran the Nvidia installer. After a reboot, the Nvidia drivers didn't load properly. the i2c_core module was not loading, unless I unloaded and reloaded the Nvidia driver. Once I uninstalled all the Nvidia related stuff from the Ubuntu repository and reinstalled the latest Nvidia driver all those problems were resolved.