I am missing an option to hide elements like "display none" for this addon to be 5/5

Useful and practical. It might be better to have a switch.

Indispensable! But I would like to see the "Pin to Toolbar" option.

ok :)
FF build in option to do this permanentliy is bounded to black or white background and text color. Why??

Error?
In Facebook also all visited Links are now slightly colored in pink. :)
An exclude list would be fine :)

Like others, this stopped working after the 94.0.1 update.

Fortunately the post by Carlos helped get it working again. His instructions that work are:

1. Disable the extension (NOT remove)
2. From Firefox Settings -> Language and Appearance -> Colors, uncheck the "Use system colors" and change the drop-down to "Always" in "override colors specified by the page".
3. Check a website that you've clicked links on to verify the color changed
4. Go back to the Firefox Color settings and change the drop-down to "Only with high contrast themes"
5. Re-enable the plugin

You should now see the clicked URL colors use the color you specified while the rest of the webpage uses whatever is determined by their style sheet.

Stopped working on Firefox 94. Carlos AM's fix worked for me - thank you!

Unfortunately, has stopped working on Firefox 94…
UPDATE:
Working again. First, I disabled the extension. Then, in Firefox's color settings, I unchecked "Use system colors" and selected "Always" in "override colors specified by the page". Used Firefox for a while, then went back to color settings, selected "Only with high contrast themes" in "override colors specified by the page" and, finally, re-enabled the extension.

It works for me (Firefox 82.0 @ Ubuntu). The only wish I'd have is to make it possible to enable/disable it on a per-site basis.

Hay que tener el historial habilitado para que funcione.