What features don't work?

If a site is generally known to work in Firefox, these are standard suggestions to try when it stops working normally:

Double-check content blockers: Firefox's Tracking Protection feature, and extensions that counter ads and tracking, may break websites that embed third party content (meaning, from a secondary server).

(A) The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

(B) Extensions such as Adblock Plus, Blur, Disconnect, DuckDuckGo Privacy Essentials, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix usually provide a toolbar button to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you sometimes need to click the button to see what's going on and test whether you need to make an exception for this site.

Cache and Cookies: When you have a problem with one particular site, especially if until recently it worked fine, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that.

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart. A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

If Firefox is not running: Hold down the option/alt key when starting Firefox. (On Windows, hold down the Shift key instead of the option/alt key.) A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

I did all the things suggested and still have the problem. It is a chess site and can't log in to my games. In Chrome I have no problems.

Can you provide a screenshot of the browser showing the issue?

When I go to my games list I click on the game I want and instead of going to the board I get a green screen as in the attached screenshot.

Looks like you used Firefox screenshot which is only for what's inside the browser. I want a screenshot showing the full browser

I'm (jonzn4SUSE)logged into the site. Challenge me!  ;-))

I use flash block, but after allowing the site it works for me. see screenshot Also, can you update your browser?

The full screenshot doesn't want to load on the page. Been using firefox and this site for 12 years never had a problem. I always update. Come to think of it my problems began on one of my last 2 updates.

You may have to use a different format for the screenshot like .gif or .jpeg because of the size limit on this site.

Also, what is the version of flash on your Mac? I see the current version of Firefox for Mac is 84.0.1. Can you give it a try?

Just loaded the 84.0.1 version and all it did was speed up the response time but still get the green screen and no board. Don't think I have Flash in my Mac. why is it necessary?

This is what I get when deny the site with my flash blocker add-on.

I removed flash from my computer and the site still works, but I still get prompted by flash blocker. Interesting...

I guess I'm going to have break out the wife's Macbook Pro... oh my goodness... standby for test.

Had to google how to do screenshots in Mac, but got it done.  ;-)) Also, Shift+Command+3 gets the entire screenshot.