This has been bugging me for too long now. My work PC never seems to remember me on any site. At first I thought there was a problem with that specific Firefox instance on my work PC until some weeks back, I experienced the same problem on my notebook.
I made some Google searches, thinking that it would be a common issue but it turns out that it’s not. I managed to get the solution though. And its quite an easy one.
The problem seems to come with the “cookies.sqlite” file in your Firefox settings folder (C:\Users\<your username>\AppData\Roaming\Mozilla\Firefox\Profiles\<random characters>.default\cookies.sqlite). The solution is to simply delete that file. If you feel that this is a too risky task for you, then just rename it to “_cookies.sqlite“. That’s what I did.
I have tested this on Windows, but I guess it would work on Linux too. For Linux, the path would be “/home/<your username>/.mozilla/firefox/<random characters>.default“.
Hope this helps some of you out there.