Annoyed that a website is doing something custom on right-click?
Did you expect the browser's context menu (Back, Reload, Save Page As, View Source etc.)?

Just hold the ⇧Shift key while clicking and Firefox will show the built-in context menu.

Edit: I had no idea this was such a widely appreciated post. Credit where credit is due: @dveditz told me about this trick a couple of months ago.