Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

[v56+] Type about:preferences#general<enter> in the address bar. Under fonts and colors, press the Advanced button. Scroll to the bottom, turn on Allow Web Sites To Choose Their Own.

Make sure you haven't enabled a High Contrast theme in the OS settings.

• We have seen reports that this can be caused by a problem with fonts like Roboto or Helvetica that

you have installed locally and that might be corrupted or are missing some variants. Also, make sure you allow pages to choose their own fonts and that you do not block remote (downloadable) fonts.

• https://support.mozilla.org/questions/1325619 Weird font on some website's

• If you use uBlock Origin make sure not to "block remote fonts".

Make sure you are not blocking content. https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/ https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

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Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

I tried to disable tracking protection and the problem is still. I have also deleted all cookies, cache and other data. Also I have opened Firefox in troubleshooting mode and the problem is still. Also enabled "Allow Web Sites To Choose Their Own. "

Make sure you haven't enabled a High Contrast theme in the OS settings.

Done

You can change this pref on the about:config page from 3 to 2 to revert to the Firefox 94 behavior.

• layout.css.prefers-color-scheme.content-override
  Dark (0), light (1), system (2) or browser (3)

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

See also this pref:

• ui.systemUsesDarkTheme [0:light; 1:dark; 2:no-preference]

You can change this pref on the about:config page from 3 to 2 to revert to the Firefox 94 behavior.

• layout.css.prefers-color-scheme.content-override
  Dark (0), light (1), system (2) or browser (3)

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

See also this pref:

• ui.systemUsesDarkTheme [0:light; 1:dark; 2:no-preference]

I tried to change this param layout.css.prefers-color-scheme.content-override from 3 to 2 and restarted the browser. The result is the same

Also I tried to create this param ui.systemUsesDarkTheme and set its value to light (0). The result is the same.

I think it has something to do with the files userContent.css & userChrome.css. For example: some styles from userContent.css appeared on the page. But deleting this files not giving the result.

I have found the reason. In Manjaro Gnome after updating you need to open "Tweaks" and in the Appearence section update Applications theme. For example I have selected Adwaita-maia-compact-dark and the problem is gone.

That was very good work. Well Done.