I had that issue with cloudflare bot captcha when trying to access a web novel website. It would infinitely loop into the "please click the checkmark to confirm you're human" thingamagic.
Initially I thought it was because I was a linux user, but I tried to browse the same website on Google Chrome and the issue went away. They were not discriminating against linux, but against Firefox, which is just as bad, if not worse.
I tried everything on FF: deleting all cookies/storage/history, disabling addons etc. It would still do this on a pristine FF. Ultimately, I admit, not being able to access websites did manage to encourage me to uninstall FF, despite it not being FF's fault, I'm tired of dealing with this kind of cr*p.