During a recent browser upgrade I found myself stuck in a bit of a corner. The Firefox add-on I had been using, Xdebug Helper, was discontinued, and the supposed replacement add-on for it didn't work correctly.
Since the functionality of this now-defunct add-on made my life a lot easier (e.g., don't have to manually append/strip '?XDEBUG_SESSION_START=default' in my browser all day long to start/stop debugging sessions) I took it upon myself to keep this functionality and perhaps get rid of yet-one-more-add-on (which pays off when upgrade time comes).
In all their simplicity, here are two bookmarklets you can use to start and stop a Xdebug session in your browser of choice. Note that if you are using a custom proxy key value then you'll need to change the '=default' part in the bookmarklet to '=YourProxyKey'.
