This works really well (most of the time) and I use it to save interesting links and some articles for further review and further research, or just to be able to search and find a link latter.
HOWEVER THERE IS ONE MAYOR FLAW - IT DOES NOT WORK IN PRIVATE MODE.
This is madness?
I have been forced to use Pocket for these sites.
Please fix it!

Why when you are adding site to categories: scrolling is so painfully slow? It is like slowest scroll speed possible LUL... At least you can bring it up with the hotkey `

非常给力，终于可以在火狐浏览器使用印象笔记了，唯一的遗憾是地址栏里中的扩展图标是黑色的，能不能绿色呀，黑色会被很多主题底色遮住，看不到印象笔记的图标，不方便使用

This add-on has been finally updated after two and a half years! It was dysfunctional in some areas, i.e. the Web Clipper couldn't save YouTube-links anymore (the Chrome version, of course, would always get updated). As a customer paying for their premium service, this negligence on Firefox was pretty infuriating. I'm thankful that this add-on works as intended again and hope that Evernote does not drop the ball again in the future.

After having problems with blocking third-party cookies and the extension not working, I got how to make it work, despite no help from the extension itself in giving instructions. You need to go to Preferences > Privacy & Security, then click on "Manage Permissions" under "Cookies and Site Data". There, you need to always allow "https://evernote.com" website as an exception. Restart Firefox and the extension should now work.