I have pinned some favorite websites on a light background of startpage. How to change light to dark. My eyes cannot approve white background. I am not pro programmer, so please give solution as for novice or intermediate user 
Tnank you at all
You can download an extension called Owl. It works great and you can change it for different websites. I can’t handle the white backgrounds either so I am using it a lot. You can turn it off and on on the owl icon in the address bar. https://addons.mozilla.org/en-US/firefox/addon/owl/?src=ss
Thank you for the Owl link. I like the new FF, but I have noticed a huge spike in the brightness of white backgrounds. I spend lots of time online, mostly with FF, and it is literally killing my eyes. Each year, my eye exam gets worse, due to this circumstance. FF seems to ignore this most serious issue.
Same here, but the Owl does help. If you have Windows 10 you can also set it to Night Light and that helps. It does make your screen have an orange look but you can adjust that.
Ok, well that helps, though I have W7, but will give it a try. On another note, Mozilla monitors deleted my below post
saying it was spam…appears they did not appreciate that I alleged they were ignoring this issue of screen brightness :).