When I click the Snipe It button on eBay, a login box with the item info appears. I enter my eBay userid and password. Then, a new Firefox window appears (instead of a new tab, even though my Firefox Preferences specify that a new tab should open), showing https//www.myibay.com/login. I doubt this is the intended behavior. But there's a place to enter my eBay userid and password, so I do so (again) and nothing happens. The page merely refreshes.

Something is wrong with your Firefox.
Please clean your cache (and cookies if possible) and try again.

The behavior should be the following:
1. You click on "Snipe it" link.
2. A new pop-up window will appear with your login.
3. Once you entered you login information and clicked submit you will see another page (not another window) with snipe information.
4. Once snipe information is entered, you will see a confirmation window.
5. You are done.

P.S.: if you already logged in once for this Firefox session, you will skip step #2.

Please let me know your eBay user id if you still have any issues after clearing browser's cache.

Thanks for your prompt reply.

I've discovered the problem: I run normally with cookies disabled. Solution: Enable cookies for www.myibay.com.

Suggest this requirement be mentioned in the Long Description at https://addons.mozilla.org/en-US/firefox/addon/5571

Any website with login (including ebay) requires cookies enabled.
But thanks a lot for catching it anyway, I'll see what I can do in this case.

<<<Any website with login (including ebay) requires cookies enabled.>>>

True, and I have eBay cookies enabled. But I use Firefox's cookie preferences to allow only those cookies I deem necessary and it took awhile before I realized myibay has cookies, too, and they must be enabled for the sniper to work. Perhaps a dumb mistake on my part, but mentioning this requirement in the Long Description would have helped me avoid it.

Thanks again for your responsiveness. And the sniper works very nicely, BTW.