Show & Hide bars
Almost all pop-ups do hide the bars (menu, status, etc). Most of the time this is wanted by the user, so disabling this feature completely in the Javascripts-Settings menu isn't advisable. But sometimes having the menu available in a pop-up is necessary. So integrating a "view bars" command in the right-click menu would be handy.
Minimize to tray
I know there is an extension that does exactly this, but the extension often doesn't get updated if a new Firefox version comes out and so has to be disabled due to incompatibility (as is the case currently with Fx 1.5). Of course it should be optionally, so users can still minimize to taskbar.