I would love to help but being an amateur I've encountered a few pain points, unless the issue is my search skills are lacking. A few days ago I finally updated my Firefox version on Debian 9 to the developer version 56 (previous 54). The problem has been finding documentation on both the Debian and Mozilla websites on how to do it the right way. Found a decent tutorial, made a back up, installed and my machine is working much better. It is old and got little memory :)
Then FF said there was an update. I got stumped. From what I could find FF sync has a limit of X bytes. I ended up looking into making a web extension but that's going to take me some time. It seems I could save the open tabs using Tabs.tab from the API, maybe. Sorry, I digress.
In short, how can I have two FF versions on at the same time, different directories obviously, with their respective icons, while manually updating them? I guess it would be to delete all the files in the dir, unpacking, and call it a day? Still need help with the two versions though.
If you read all of this, thank you.