If you're a developer who uses the XDebug PHP debugger, you probably already use a Firefox extension called XDebug Helper, which provides a convenient toggle switch for enabling debugging. You probably have Firebug installed too. Here is a method for setting up keyboard shortcuts to toggle them on and off (I use F1 & F2).
First, install the keyconfig Firefox extension (unfortunately it doesn't have an official page). Click Tools->Keyconfig... and you should get the following window:
