I get models from 3Dcontentcentral.com pretty frequently, after first hearing about it on this group. I'm also a big fan of Firefox, and I couldn't find any search bar plugins for 3DCC, so I made one. You can find it here:
formatting link
It doesn't include a sidebar display of the results; this isn't a feature I ever use myself, and I'm not quite sure how to set it up. If this would make it more useful for you, let me know and I'll spend some time to figure out how to use it (or go ahead and write the fix yourself, and I'll update the code). The search icon is messed up, I'll fix that when I get home and have access to a real graphics program.
Anyway, feel free to give me any comments, complaints, or suggestions. I hope it's useful!