This means malware infections and you need to boot in Safe Mode to clean out the infections if you want to continue to use your computer. This is something FF forum can't help with and you need to get a computer shop to fix this malware problem.

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

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

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.

Kudos to Norton, they blocked a malicious ad from loading!

More info on this detection: https://www.symantec.com/security_response/attacksignatures/detail.jsp?asid=28173

It's possible the attackers are not targeting Edge users right now. The attacks seem to come in waves as they discover a new tactic that tricks users into clicking or bypasses the most common protections (ad blockers using popular filters).