Add capability to interact with installed addons/extensions

[b4handjr]

It would be nice to click on an extension after it is installed, say Testpilot or Containers.

[b4handjr]

@davehunt I am thinking of putting this within the addons.py.

[whimboo]

I want to note that this is NOT a core feature of Firefox, and most likely warrants it complete own section.

[b4handjr]

@whimboo good point.

[b4handjr]

I got this to work pretty well but I can't actually check that the extension that is clicked actually works because foxpuppet currently does not support any sort of tabs. See my comment on #69

I closed #69 but will repoen with a better implementation. I think I will have to hold off on this until tabs get landed.