Websites say that Firefox is outdated or incompatible even though it's the latest version https://support.mozilla.org/en-US/kb/websites-say-firefox-outdated-or-incompatible

This article is no longer maintained, so its content might be out of date.

It is possible that you have disabled some Firefox features that the website requires.

Are you possibly using Private Browsing mode or otherwise made changes to block content ?

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows an highlighted shield icon at the left end of the location/address bar in case Tracking Protection is blocking content.

• click the shield icon for more details and possibly disable the protection

You can check in the Web Console what content is blocked

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

Strangely enough, I made no changes to Firefox and the problem resolved itself. It must have been a problem on Discover's end and I jumped the gun instead of waiting several hours.

Thanks to all who replied.

Hopefully, it stays gone. Please flag your last post as Solved Problem as this can help others with similar problems.

If this happens again then try some basic steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" for websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Manage Data

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems