There is an article over at TechCult titled 10 Weird Browser Extensions. The list does include some really odd extensions, like one to block YouTube comments with ALL CAPS or excessive punctuation!!!
There are some useful ones in the middle of the pack though. Like the FireNES one:
You don’t need extreme hackery to protect yourself from the rest of humanity – just find something better to do and you’ll never need to deal with those annoying fleshbags again, and it doesn’t come much better than FireNES. Two thousand ROMS all ready to go in a browser toolbar. Claim that isn’t better than constantly refreshing an e-mail window and you’re a filthy liar.
The Java application doesn’t deliver the smooth emulation of Nestopia, but for somebody stuck in some kind of work-like environment where they can’t install software, it’s perfect. Not that we encourage reliving the joys of your childhood rather than doing those really interesting spreadsheets, of course.
Check out the full article to see all the other extensions that were included in the list.