See https://bugzilla.mozilla.org/attachment.cgi?id=466515

I implemented something like this for the account manager bug: https://bugzilla.mozilla.org/attachment.cgi?id=468724&action=diff The basic idea there was to place the account manager button above the identity block where the account manager button is made up of 1) a content box, 2) a box that is svg:clip-path to a triangle with the same background as the context box, and 3) another box clip path triangle that forms the darker border. However, it might make more sense to have the clip-path cutting away the identity button as multiple icons need to integrate with the identity button.