Browsers and App Store Locking Up

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I don't know if this is the right forum, or even if there is one for this, but my Mac started acting really strange tonight.

All of my Internet browsers and the Mac App Store seem to only load pages for a few seconds and then become entirely unresponsive. When I command Q to quit, the application closes, but the dot remains in the dock so that I have to force quit. I have restarted many times and tried repairing disk permissions. Has anyone ever heard of this?

 

I hadn't tried that, since browsers I never use were broken and I couldn't clear the cache of the Mac App Store.

When I got up this morning, everything worked fine. I can't think of a single reason why my computer would have been acting so strange, but Firefox, Chrome, and the App Store aren't freezing, and I can quit them without them all locking up.

This is the most bizarre thing I've ever seen happen and if it happens again I'm just going to reformat the whole thing.

 

I did try things other than browsers, assuming in this case the Mac App Store is a browser. But only browsers have been locking up. Everything else has worked fine, and even other apps that connect to the internet, like Adium, work great.

The issue has subsided some, but is still causing problems off and on. Could a problem with the hosts file affect this? It's the only thing I can think of that would affect all browsers at once.

I think now's a good time for me to back up and reformat, though. Best way to prepare for the Lion upgrade, since it's diskless.