Just what i need and it is working as described.

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.