On the Windows task bar, a blinking icon means the program wants your attention. Sometimes because of an error. If there looks to be no problem, don't worry.

¡Hola Mike!

Could you please record a video of the behavior using https://www.techsmith.com/download/jing/ ?

Does this adversely affect your browsing in any way?

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

¡Gracias!

Can't start in safe mode because the concern is in clicking on the icon to start Firefox. If it is already started, I'm past the icon already. Note that I even changed icons and whatever one I used also flashed. I tried uninstalling and reinstalling Firefox, but I kept my profile and bookmarks and the problem did not go away. I had stored the book marks and profile on the desktop and I did not have to re-install them. They were already there when I opened the new Firefox that I had installed. I could not record the issue either. Any other ideas? Could there be a virus/malware not detected by Norton, Malwarebytes or Spybot, all of which have been used to scan the computer? What about a keylogger?

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.