. . . and can't fully read screen; something about icons.

Hello,

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Thank you!

Did this problem with the video just start? Can you tell when?

If you have Windows 10 N or KN then you may not have the Media Feature Pack installed. https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows

https://support.mozilla.org/en-US/kb/fix-problems-images-not-show

http://kb.mozillazine.org/Images_or_animations_do_not_load

https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows

https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues

https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox

https://support.mozilla.org/en-US/kb/troubleshoot-issues-with-plugins-fix-problems

https://support.mozilla.org/en-US/kb/warning-unresponsive-plugin

Screenshot

Just today I have vision problems and colour blind

It appears you have an extension called "Youtube Audio Extension" installed. Try disabling it. 1. Type in about:addons in the address bar 2. Disable "Youtube Audio Extension" or something with a similar name 3. Go to the Youtube video again and check if the video plays

thank you for your help

Problem solved

Well done both of you.