I had the same problem. It was caused by a form filling add-on.

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?

Yes it is.

I started it up via Safe Mode and nothing much happened. I also tried deleting cache & cookies and reinstalling (I don't usually reinstall applications but I tried this too)

Anything else?

NOTICE: This is happening on Microsoft Egde too. What could be the problem causing this?

LukaTrbovic said

NOTICE: This is happening on Microsoft Egde too. What could be the problem causing this?

Do you have a dynamic or static IP address? If it is dynamic, try unplugging your modem for a few minutes and see if you get a new IP on startup. If it is static - maybe you could try to contact Cloudflare?

https://support.cloudflare.com/hc/en-us

Happy112 said

LukaTrbovic said

NOTICE: This is happening on Microsoft Egde too. What could be the problem causing this?

Do you have a dynamic or static IP address? If it is dynamic, try unplugging your modem for a few minutes and see if you get a new IP on startup. If it is static - maybe you could try to contact Cloudflare?

https://support.cloudflare.com/hc/en-us

I have static IP. I'll try contacting them. I was looking a bit on their forums and found nothing. I'm going to make a topic.

Thanks.