Does not work well with DarkReader. I don't know if this has anything to do with the implementation of the addon itself...

Finally found a sticky version that has all the properties I was looking for (can be locked so it doesn't move on page and has solid color).

Would be nice to add black color for sticky background!

Thanks for this nice addon <3

---------------------------------------- edit after 9 days of using ----------------------------------

Seemed great at first but it turns out that the text moves up and down when I move focus from the note. The text also mixes in the same line so when I return to my notes they are completely disordered. I have to degrade from 5 and give it 3 stars :(

Great add-on, would give 5 stars, but I disabled it because it needs to "Access your data for all websites" and since this permission allows the extension to "read the contents of any web page you visit, as well as the data you enter into these web pages, such as usernames and passwords", it's not worth it to me.
I really don't understand why so many extensions need such a high level of permissions in Firefox, it's as if your gardener would need access to your bank account to do his gardening. Nope.