What is the answer to this question?? 66 people have the problem but i can not see an answer.

Please provide more information (e.g. screenshot) if you have this issue.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

Did anyone find out where the answers are to this question??? What is the blue line?

Do you still see that line if you start Firefox in Save mode?

• https://support.mozilla.com/kb/Safe+Mode
• Help > Restart with Add-ons Disabled

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

No No No - No Extensions were installed. It was a fresh copy of firefox when this occurred. No more safe mode stuff.

When it does occur it can be "fixed" be restarting the browser.

The blue circle connected to the blue line with a white line around both in between tabs appears to be related to "tabs" or minimizing windows.

There is a lot of third-party or security software that installs extensions globally, so with a new profile there may still be extensions installed.
I'm not sure if that is also the case on Mac, but it does happen on Windows and Linux.