I found a Firefox add-on that provides an eBay Toolbar, thumbnails even for products whose sellers didn't pay for it and some other goodies. My bet is that within one month they'll be sued.

Why?

1. Trademark infringement: Using the registered trademark eBay in a manner that isn't sponsored or promoted by the company. (In fact, it probably pisses them off...)
2. Possible DMCA violation allegations: eBay charges extra for thumbnail fees; this is a means of circumventing those fees.

I love the idea and think it's great, but it just seems that they're begging to be sued. Hopefully even if they are the Firefox extensions will continue to work for sometime, though. ;)