If you didn't notice from reading my psp posts, I love classic gaming. I'm also a Firefox user, and always on the hunt for good addons like the rest of you. Thank god for FireNES, an awesome addon for Firefox that gives you ready access to a massive repository of NES games.
After you install it, customize your toolbar and add the FireNES button to give yourself one-click access to the sidebar. The full ROMs list is massive, The toplist contains the 100-or-so most played titles, and you can add any game to your list of favorites with a simple right click.
Best of all, you don't have to hunt down ROMs on horibly cluttered, scam-laden websites. Awesome.
The only possible downside to all this: habla usted español? The developer's page is Spanish only - not a big deal, the install link is easy to find and you can always run it through your favorite translation app or download it here