Thanks for the feedback! Your use case of saving a window's worth of tabs makes a lot of sense. In the new update of this extension, tabs are grouped by what window they were in and you have the option of restoring to your active window or a brand new window. I'd love to hear your thoughts on the update if you get a chance. Thanks again for the review.

Edit:
I really appreciate you taking the time to try this extension again. I can't seem to replicate the problem of improper rendering on my machine. If you have time, please file an issue (https://github.com/avbhatt/tabs/issues) with your Firefox configuration. In terms of "Save" feedback, there should be a flash to "Saved!" after clicking.