Could bad RAM be causing this computer problem?

I have a 3 year old Macbook. Yesterday it randomly started freezing. There doesn’t seem to be any pattern to it except that opening new tabs in Firefox seems to set it off pretty consistently.

I booted in safe mode without event and ran fsck, and my hard drive is coming up okay, so I don’t think that’s the problem. A few weeks ago I had to replace one of the sticks of RAM. Is there any chance this is being caused by bad RAM?

Any other diagnostic help would be much appreciated. I really do not want to have to buy a new computer.