I use Firefox 79. I have removed all the extensions except my antivirus (Avast Ultimate) which includes a VPN but the VPN is currently turned off. I have Firefox 79 installed on two computers, one of which connects by CPL ("powerline adapters/homeplugs") and the other connects to the router by an ethernet cable. My Firefox settings are identical on both machines and I have no Captcha problems with the one using the ethernet cable. I also completely turned off my home network and reset it - fibre optic box, router, both computers, and unplugged the CPLs - and then restarted them from the optic box forwards one by one. It made no difference, the CPL problem still exists. I sought help on the Microsoft Community Forum and sent the two blokes I was working with all the above info and they concluded that the problem wasn't with the CPLs which, incidentally are TP-LINK, model TL-PA7010P(KitFR) with the Version 3 software. All three lights on each of the CPLs are solid green. I have also informed TP-Link France of the problem and I'm waiting for their reply. Following advice from one of the blokes on the MS Forum, I ran a Speedtest.net on the CPL machine and the results were: downloading 91.99Mbps and uploading 87.47Mpbs and the Ping response was 20. (This is all nonsense to me but may help you.) Both people on the MS Forum concluded that the problem does not lie with the CPL. I'm going to replace the CPLs with a 30m ethernet cable (less aesthetically pleasing and more encumbering) to see if that resolves the issue.