I didn't have websites outright breaking on FF like solardev, but I had other issues with it, like cloudflare getting me into an infinite loop of asking me if I'm human and not letting me browse the website. This happened even if I deleted my firefox profile and started fresh with no extension. Note that this behavior of Cloudflare is highly dependent on the settings of their anti-ddos stuff, some websites have it set on a higher level of defensive behavior than others, I didn't have this issue everywhere.

This wasn't due to my computer's IP, the problem went away the moment I browsed the same website with Chrome, and this time I wasn't even asked to click the checkbox to prove that I'm human.