I know, I know, this used to be answered with a simple yes, I know that. But nowadays with the whole Webextensions disaster about to happen to Firefox, I wonder if it is still possible to avoid Firefox updates, because I've seen cases where the automatic update was TURNED OFF but somehow it still updated and it wasn't possible to get some add-ons and/or extensions back.
To clarify: this is a case where browser updates kill your add-ons.
Follow up question:
Is the only way to do this via the Portable Firefox-option?
Read this complaint by the developer of the popular Firefox add-on DownThemAll! why he is quitting Mozilla after 15 (!) years: