This extension is superb on a PC!
Pros:
* Saves tabs for easy access later
* Can import/export tabs for use on another device
* This extension doesn't scrape and sell your data AFIK

Cons:
* Currently on Android Firefox some features such as adding current tab or just one page at a time don't seem to be available, but I know this scenario is probably kind of rare.
* Firefox on Android currently doesn't let OneTab save inactive tabs, so you have to open those tabs to make them active and then save to OneTab

I love the pros enough that I'm ok with the cons and can just work around them.

very useful

Amazingly easy to see and quickly delete tabs that I'm not using anymore. A godsend for a tab hoarder like me. Also makes it easy to copy a list of URLs from a particular window!