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 a purple shield instead of a gray shield at the left end of the location/address bar in case Enhanced Tracking Protection is blocking content. You can click shield icon for more detail and possibly disable the protection. You can check the Web Console for messages about blocked content.

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.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 or userChrome.css 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

It's facebook.... they are forcing mobile type interface...cannot get into facebook using firefox...they say no longer supported !!!!

I checked Facebook and have no problem to login with Firefox 82, so 81 should work as well, so there must be something in your setup (current profile) or a problem with other software on your computer if you have a problem.

You can create a new profile as a quick test to see if your current profile is causing the problem or if something else is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

I have no problems with other sites. ver 8.1.01 It specifically says firefox is no longer supported with facebook and tries to make me use a mobile browser (on a PC???) I will not use the NEW facebook and prefer the classic view and I do not trust Facebook. When facebook changes things like this, it is BEWARE of what they are doing.

So you use an extension that pretends to be an older Firefox version to force the old Facebook layout and this is no longer working as Facebook has stopped supporting the old layout ?

What???????? I'm using firefox now. I haven't done anything. Facebook just started this. I can go to a friends mac and log in and no problem. I was on FB the day before and nothing changed. I just get this message from Facebook This browser is not supported.!!!! I don't like updated Firefox as the extension/plugins from 3rd parties stop working so there is no point. FIrefox used to be a great browser but the more they do to it the more they mess it up. Facebook is not worth the hassle and they cannot be trusted with what they are doing.

this isn't strictly related, I've just logged into FB after a crash, and FB has updated my profile layout to the new style.

does anyone else hate the new style? it's completely reducing functionality.

it's as if (and I totally believe this) they are trying to take functionality away from the user (yes I know I just repeated myself)

sell your data - yes useable website - no ? [xcuse the thread hijack - edit, actually reading thread in some detail and it is a bit relevent]