Javascript (I think) content not working

Every so often certain pages or buttons will stop working properly. These include Google Maps (typing a location in the box and pressing enter does nothing, and there's no autosuggest either, and it's impossible to drag the map to move around) and Twitter (the buttons, such as the "New Tweet" button stop working). Buttons on various other sites fail to work too.

The solution is simple: I restart Firefox. But then it comes back, perhaps 10 minutes later, perhaps 20 minutes, perhaps 2 hours.

Any idea what could be causing this and how to solve it?

Tim