Recently Firefox starts to show annoying message:
It looks like you haven't started Firefox in a while. Do you want to clean it up for a fresh, like-new experience? And by the way, welcome back!
This is shown if your user's profile hasn't been used for 60 days. Or restarted - because that information comes from Services.appinfo.replacedLockTime. Which I very rarely do.
So how to get rid of this message. I had to download source code and find that specific part, but after quick search I found the way.
Open about:config window and create new boolean
browser.disableResetPrompt and set it to
true. And that is all.