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Almost ever video, since switching to Firefox, comes up with a flashing red and black sign: FLU.

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Since switching to Mozilla Firefox, a couple of days ago, almost every video we try to view shows a flashing black and red sign FLU. We have no idea why this is happening. We have Norton Antivirus running and it is showing no problem. What does this mean, and what should we do? Thank you.

Since switching to Mozilla Firefox, a couple of days ago, almost every video we try to view shows a flashing black and red sign FLU. We have no idea why this is happening. We have Norton Antivirus running and it is showing no problem. What does this mean, and what should we do? Thank you.

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Please provide a screenshot of that.

https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

It is best to use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed a maximum file size of 1 MB.

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Is that an image that is superimposed on that video or is that shown instead of the video?

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).

Endret av cor-el

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The flashing FLU sign appears beneath the icon of the video we wish to watch. As soon as we click on the icon, the FLU sign appears and starts blinking; it is impossible to access the video.

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Did you try Save mode?

  • Help > Restart with Add-ons Disabled

Check the connection settings.

If you do not need to use a proxy to connect to internet then select "No Proxy" if the default "Use the system proxy settings" setting doesn't work.

See "Firefox connection settings":


Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":


Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

See also: