What does it look like? Here's a reference image for no anti-aliasing, grayscale anti-aliasing, and "Windows ClearType" subpixel aliasing. Which of the lines do webpages in Firefox look like, and which is normal for your system? (You may use the "browser rendering" test below the reference image on the linked page to compare.)

This may be result of disabled or not functional hardware acceleration, where the text rendering cannot use the full GPU power and thus reduces the complexity of drawn elements to work with the limited resources.

You may try Safe Mode (temporarily disables HW acceleration, extensions, custom themes etc.), see if the issue persists and report it here.

Hello,

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Thank you!

Type about:preferences#general<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

Fonts Information - Detected via Flash http://browserspy.dk/fonts-flash.php?detail=1

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

Also see: https://support.mozilla.org/en-US/search/advanced?q=fonts&language=en-US&product=firefox&sortby_documents=relevance&a=1&w=1

I did a Windows 10 update and it fixed the problem. Thanks

That was very good work. Well Done.