If you’re about to install a Firefox extension, you’re out of luck: The Mozilla add-on site is down. Of course sometimes it’s not the destination, but your connection – so how can you know? A very appropriately named site: downforeveryoneorjustme comes to your rescue:
The site will quickly tell you if you have a problem, or, as is the case now:
Huh? doesn’t look like a site on the interwho.
(As good a name they picked, it’s longish, you might want to bookmark it)