Think its Javascript settings, but depends what browser you're using depends on the support. Just did a search for browser support for JavaScript, and google have a nice little page to make sure it's switched on.
As the page says "google ads" are in JavaScript, so if you visit a lot of pages that have missing content in the side it's enabled.
This can be a good thing as your screen won't be full of ads when you visit certain pages, but on the other hand somethings will just not work.
Or as Spud said, change your browser there are loads out there, or maybe your browser just needs updating.
google link for info and how to is
https://www.google.com/support/adsense/bin/answer.py?hl=en&answer=12654Hope that helps.
Davey
Edit 19:54
Follow up, read this post at lunch time, didn't realise that Spud had put more info on, as I didn't re-read.