Thank you for the review and suggestions!

I do like the idea of having the option to not load all the tabs at once. Though, this can be quasi worked around by selectively opening tabs. In the context you are thinking of I see there being an actual underlying "session" that is being maintained. When I re-write this plugin to clean things up these will likely get implemented along with the auto saving functionality.

As for having the presence of mind to recover a crashed session, that is somewhat a challenge to implement and from a plugin standpoint probably harder yet. I'd need to research it a lot more.

EDIT 02/01/2020:
I have more or less refactored my code and am relatively happy with how it's structured. Per your suggestion, I added in the number of tabs in a session to the session list item fields. I hope you've played with the selective load option to resolve your issue of loading a session causing all the tabs to load at once.

I haven't gotten to the last suggestion you had where one could set a timer to auto save sessions or have some kind of recovery mechanism if/when Firefox crashes. Either of these will require more tweaking with how this code is implemented. I made a booboo in using SweetAlert and how I set it up. My refactoring has mostly linearized the flow between the files but decoupling SweetAlert is still a task I'm not looking forward to.