For years, I have used FF Portable (on Windows 7). However, I ALWAYS disable the auto-update feature. This is because the update process always tries to create another copy of my user profile, bookmarks, and add-ons under these locations:
C:\Users\[logon name]\AppData\Local\Mozilla
C:\Users\[logon name]\AppData\Roaming\Mozilla
Note: The same thing happens if you set FF Portable as the Default Browser and Windows tries to start FF Port like a normal application. A second set of application files are created.
The existence of a duplicate location for these files fouls up Firefox Portable; eventually, you must delete and re-install it.
Unfortunately, in version 63, Firefox has no menu-based option to disable the update prompts. You can stop the application from automatically downloading updates, but you cannot stop the application from constantly nagging you about the update.
In an effort to stop this prompt, I have gone into about:config and have made the following changes:
app.update.auto = false
app.update.service.enabled = false
app.update.download.promptMaxAttempts = 0
app.update.elevation.promptMaxAttempts = 0
None of these changes have worked. Does anybody have a better idea to stop this prompt?