A keeper Rated 4 out of 5 stars
I've tried lots of extensions, and I don't keep a lot of them, but despite its simplicity, this one's worth keeping installed. So many, many sites go from hours of checkbox-clicking drudgery to an instantaneous snap that I groan when I'm stuck in a browser that doesn't have this installed.
One minor warning: Checkfox v0.6 seems to have broken compatibility with Firefox 2.0 (tested with Firefox 22.214.171.124/Win32). v0.5 works fine, though. I haven't tested in Firefox 3.0 yet, but the developer claims v0.5 and later work with it.
Get this extension --- you'll be glad you did!