This simple extension makes it easier to switch between the single process mode and the multi process mode of Firefox Nightly / Developer Edition / Beta. The multi process mode is currently being switched on in the release version of Firefox.
The toolbar panel provides two buttons for restarting with/without multiple processes, one spin button for setting the maximum number of content processes and one button for restarting in safe mode (without extensions). The toolbar button shows a yellow thunderbolt when the parent window is in multi-process mode.
Process Toggle has been available since August 2014. Further development of this extension has been paused as of February 2017.