Thanks！
But can be set per site

Было удобное расширение, позволяющее приводить в норму сайты с кривой раскраской. Однако сейчас сглючило - весь интерфейс управления не помещается в форме расширения, потому невозможно нажимать на кнопки Text color, Background color. В общем потеряло работоспособность. Видимо зря позволил ему автоматически обновляться.

The popup window displays only text and part of the background setting. I just wanted black text but links get changed to GREEN! Yikes. (Firefox 89, Win10 2004, 10-in screen) Using "No Color" instead.

using this add-on changes graphics on web pages, for. example a weather chart that shows bars for a range of temperatures changes to dots. 4/18/21: thank you for your reply. The add-on is not really functioning. I wish I could attach a screen shot. For example, I do a google search, on the top there are usually made up questions with the down arrows to the right. I picked text as black, background light pastel green and the links blue. The text was changed to black (the little arrows have disappeared) and the links, which were originally blue, turned black. I am glad if this works for others but for me it is a mess. Good luck. Added a star for your addressing the issue.

Weird and non-intuitive interface to change the colours ... didn't like it. Removed add-on