Firefox window always starting maximized [duplicate]

Solution 1:

Well blow me down with a feather! To answer my own question, and help others, I have just come across https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1730410, including :

Almost all applications (Firefox, Nautilus, Google Chrome, PyCharm, Skype, Calendar and other) opens in maximized size if it window size was larger than some value (more than about 80% of display width and height) when application was closed.

and

This is indeed a mutter "feature". Use 'gsettings set org.gnome.mutter auto-maximize false' to turn it off.

No wonder it seems intermittent: if I close my window when it's 79% size it restores but if it's 81% it maximizes! Who dreams up such unintuitive behaviour?!

I confirm that making the FF window smaller before closing solves the issue. For my part I have run the suggested gsettings command to change the GNOME setting and now I can close from any size and it restores to that size as desired.