Firefox Trojan
When launching Firefox Malwarebytes reports a trojan and shows blocked website verifications.io This happens just about every time. Wikipedia tells me "Verifications.io is a defunct email-focused technology firm whose primary practice was to validate email addresses for email marketing platforms. The company's platform allowed for email marketing firms to submit lists to the company, which would verify the lists for valid email addresses."
Wubrane rozwězanje
Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile. Make sure you stay signed out of your sync account when testing.
Toś to wótegrono w konteksće cytaś 👍 0Wšykne wótegrona (5)
You can check that those pages aren't set as multiple homepages.
You can check the homepage setting in "Settings -> Home".
Firefox supports multiple homepages separated by '|' (pipe) symbols.
Do you have a history entry for that domain that allows to use "Forget About This Site"?
Many thanks to cor-el and zeroknight for their suggestions but they didn't solve the problem.
Wubrane rozwězanje
Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile. Make sure you stay signed out of your sync account when testing.
May check the about:networking page. You can also enable network monitoring in the Browser Console and leave the console open when you restart the browser to check if request to this origin show up.