Please consider turning on send info to Mozilla before posting a question. This helps us help you. If you check your Update History it is possible you received a update to Windows Defender. Or it just realized that your Firefox is now a different version since running the current version. Microsoft wants it to be your A/V & Firewall. It does none of it very well. Since found the rules, delete them and create a rule to allow or wait for it to again popup and this time make the appropriate choice to allow for both TCP/UDP. I strongly suggest getting a proper Firewall that monitors TCP/UDP to Firefox and blocks ones that are in their rules that are actually malicious. I run Norton Security and am blocking thousands of malicious requests daily to both ports. It is also advisable to run a anti-malware program at the same time. I run Malwarebytes and it blocks stuff that Norton does not catch. Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed. Please let us know if this solved your issue or if need further assistance.

See also: *https://support.mozilla.org/en-US/kb/Firefox+makes+unrequested+connections