Load temporary add-on from run command

[kumar303]

The install/run command landed in #90 and by default this creates a temporary profile, opens Firefox, and loads an extension. However, we have a button for this same work flow in Firefox. It would be great if you could load a temporary add-on into your current running Firefox from web-ext.

[kumar303]

This is not required for auto-reloading

[kumar303]

Correction: as of https://bugzilla.mozilla.org/show_bug.cgi?id=1269889 it is now required to first install a temporary add-on. This is because the implementation of reload was becoming too hairy. It was easier to re-use the temp-install functionality.

[kumar303]

This is mentioned in the docs now: https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Getting_started_with_web-ext#Testing_out_an_extension

There is also a Firefox 48 section to explain how to run an extension there (since it won't support temporary add-on loading from the remote debugger): https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Getting_started_with_web-ext#Testing_in_Firefox_48