Best DarkMode extension so far for Opera on Ubuntu, works properly. Would be nice additional feature to have settings applied to 1 specific website. And have other/general setting for other website. Reset button. Number indicator next to each slider 0-100.
For FireFox on Ubuntu not so good... Stress testing with 32 open windows/couple of 100+ tabs open >> FireFox stopped working all together Remove the add-on >> FireFox works again