Change the order of the tab context menu items and separators. THIS REQUIRES TAB MIX PLUS. First, go into Tab Mix Plus Options > Menu > Tab Context Menu... and select the items you want to appear in the menu. I put the instructions in with the code because I thought it would be handier in front of you rather than having this page loaded the whole time you are messing around with it. Follow the instructions and you shouldn't have any problems.
The Menu Editor (http://menueditor.mozdev.org/) is easier to use and can change all context menus.
.ad {
/* Your ad can be here instead. 10K unique visitors for $5/day. Mail me. */
}