Really usefull addon here, with only one big exception. Every now and then (usually when firefox updates), all your saves will be wiped.
Lots of folks have this problem and commented on it without resolution. It is kind of surprise that you need to save your saves to live your life in peace with this software. Given a bug is here for a years now, one would expect it to be finally fixed, but devs are silent and source code is closed.
Since it's the main thing (to my knowing) why this addon is uninstalled, I can easily imagine that this exception can lead to extinction of this extension.
Here are testimonials of other slightly pissed, hissed and by this issue kissed people :
"TL;DR OneTab extension has major bug"
"ppl complain daily on their app reviews that they lost tabs"
"OneTab dev(s) ... have made the user experience uncertain and risky"
"I will never, NEVER use OneTab again!"
"All beware the empty promises of OneTab!"
So please do something about it, for good of all your fans.