Since updating to 10.5.3, I have noticed some browser issues.

Firefox is using 7 - 10% of my CPU even on mundane pages. The MacForums home page uses 7 - 13% CPU. Displaying exactly the same page in Safari uses less than 0.2%

I have no plugins or extensions running on FireFox, apart from Adblock (I also have SafariBlock on Safari)

As for Safari, it has become a little unstable. In fact it crashed as I clicked 'new post' just now. Repeating the action didn't result in a crash. Watching the ABC player earlier tonight also crashed Safari (it never crashes Firefox, but Safari has gone a few times).

Any suggestions?