My productivity has improved so much with being able to have different tab groups for work, personal, research, volunteer work, etc! Great way to get in the zone and not be distracted by other parts of your life.
I have had it crash a few times, but when I close firefox and reopen it, all my tabs are still there so it's not a big deal. Be aware that it makes backups in your Downloads directory (starting with STG); you can delete the old ones at any time or disable this in settings.