Oh wow, finally, great. The inability to manually install add-ons was also a major annoyance for add-on development (at least for me), because without that you

Oh wow, finally, great. The inability to manually install add-ons was also a major annoyance for add-on development (at least for me), because without that you were restricted to temporary add-on installation via devtools, so you couldn't really seriously test drive your own add-ons for any extended period of time. (Or attempt tracking down some rare bug.)