Thanks to some recent improvements by Kris Maglione, add-ons built with Firefox’s add-ons SDK are now much faster to start up and shut down. For users with multiple add-ons installed, this can make a large difference. For example, one user reported the following.

Your mileage may vary, but these improvements have the potential to benefit many users. They are present in Firefox 50 (currently in Beta, and due for release on November 15) and all later versions.