Firstly, thank you for going to the effort of making this add-on.

I have just one request, and here it is as a User Story:

As a Firefox user,
I need to have new sessions that are opened by clicking a link *outside* Firefox restore tabs as expected AND add the tab just opened by click the link,
so that the page I wish to see by licking that link is now open, and I don't have to waste time going back and clicking the link a second time.

Acceptance Criteria:
GIven Firefox is closed,
when I click on a link in, say, Outlook,
then Firefox opens,
and tabs are restored automatically according to how I've set up TSM,
and the new tab is added and has the focus.

I'm sure you're sick of comparisons to the old Session Manager, but this describes its normal behavior.

Good luck, I hope you can manage to add this feature. It'll be much appreciated.