Hello,
The Firefox Bookmarks Toolbar is initially hidden. (I used the term "Menu Bar" above, but I should have said Bookmarks Toolbar.)
Here is a good 3-minute tutorial video:
https://www.youtube.com/watch?v=Qvs8aEkVo48
Or, you can follow these steps:
1. To enable your Bookmarks Toolbar (on Firefox), Go to View-->Toolbars-->Bookmarks Toolbar. If it is properly enabled, you will see a checkmark next to "Bookmarks Toolbar."
2. Then you can drag the Slam-It icon up to that bar, and it should stay in place.
3. Then when you are on an eBay listing page, click that toolbar.
Let us know if we can help further!
bidslammer