Are you using any programs/add-ons that block content?

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Image problem seems to have been resolved. The video problem is still present

It could be the work of one of your add-ons. Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

I cannot play the video in safe mode either due to needing to install Adobe Flash Player, which I suspect is the root cause of the black screen.

Flash is a plugin. Plugins are not disabled in Firefox Safe Mode.

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Go to that message, and use the Undo link to its right.

Can you post your troubleshoot information including a list of your extensions?

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

Try to uninstall Adblock Plus because this extension has been reported to cause issues. You already have uBlock Origin and one content blocking extension should be sufficient.