Yes, I’m having problems too. Months ago I downloaded the latest version (at the time). My task manager will tell me that it is using 100% CPU usage.
If I walk away from the computer for a couple of minutes and then start using the mouse again, firefox freezes up. It’s a pain.
I wrote a message/question on their help board on a thread where others were having the same problem. They blew it off. Said the problems must be individual not systematic. Said to download the latest version and to change/check your user profile. I haven’t gotten around to screwing around with it.
Over the past couple years there have been a lot of issues cause by third party apps who I swear are intentionally not updating for MS security changes and upgrades. Flash, java, adobe, and some others have not kept up as fast as they should, or they don't auto update and you have to go and get it from the distributer.
Adobe and flash are two major culprits, and java has a habit of not running older apps with the newer versions and you have to have the older versions as well.
Just some experiences......