Moving your toolbar icons around is a great way to consolidate Firefox's interface, but you may not realise that those icons aren't just constrained to the toolbar. They can actually go up on the tab bar, too.
Lots of people like having quick access to Firefox features right from the toolbar, but if you start running out of space, you might be wondering what to do with all those buttons. You used to be able to put them in Firefox's menu bar, but since Firefox 4 put the tabs on top, you might not have realised that those toolbar icons can still be dragged up, off the toolbar and right onto the tab bar. See the image above, where the Greasemonkey and LasPass icons are above the toolbar, leaving more space for searching, URL monitoring, and other important stuff. It's a simple tip, and one you may have already known about, but we had a little facepalm moment when we realised you could do this.
Toolbar Icons on Tab Bar [Firefox Extension Guru's Blog]