Eric, thanks so much for creating this extension! People are fed up with the current crop of programmers who ongoingly impose unwanted tweaks down our throats against our choice. I had wasted too much time trying out dead-end solutions until I found your add-on via a Reddit respondent. For example my resistFingerprint was already set to "false" so the latter suggestion was a dead-end for me. And manually tweaking the browser margins (via the double-arrow cursor) also had failed to remain that way upon restart. Thanks again!

make all works... source : https://www.reddit.com/r/firefox/comments/pmo1gz/open_firefox_maximized_everytime/ ...
- in my case, about:config > privacy.resistFingerprinting == true...
- have a non standard windows size make you tracable... with a unique browser fingerprint

Great if you have privacy.resistFingerprinting enabled

For fellow LibreWolf users or anyone who turns on "resist finger printing" for their Firefox browser, this is a simple yet must-have extension!

Fantastic!! And it's open source.
I wish it was quicker (or instantaneous).
But well done!

Works perfectly! I installed it because new windows won't open maximized when resist fingerprinting is enabled.