It started suddenly with me. It seemed flash related. but I had also download some torrent software that wanted to install toolbars and other stuff. I thought I had refused to allow those to be installed.
Nevertheless, I started getting all these flash animated ads. Pure annoyance. As I was using Firefox, I found an add-on called AdBlock Plus.
Installing Adblock plus solved it. No more erratic cursor, selecting everything my cursor passed over, or non-responsive clicks. Even problems getting Finder to work properly.
I had tried restarting to fix it, and that didn't help, so I'm pretty sure all those crappy ads were the cause. Especially bec of the stange toolbars that the torrent tried to install. I totally lost control of my entire computer, not just Firefox, or web browsers.
AdBlock plus seems to be a really good thing. It doesnt block ads that comply with their guidelines, by default, although you could disable them too. Their theory is that is websites are rewarded for complying and not throwing up annoying ads that block what you are reading, or that crawl across the page, or take a permanent position on the page, they will not try that stuff.
Try it, I hope you like it,