Welcome to the community! 
First thing’s first: Do you know how straight-forward, easy, and convenient it is to switch from Chrome to Chromium like you never even switched?
Can only imagine how difficult it would be to try to convince you to switch to Firefox.
Next: I’ve gotten these error messages too in Firefox, and usually an update fixes it.
I’m guessing your AUR package may have just been out-of-date by a few hours to a day.
Another thing may be if you have hardened your browser a bit by disabling Javascripts or using extensions which add a layer or so of privacy or even ad-blocking. Websites that do advertising obviously don’t like that.
And the only other thing I can think is just the fact that you are using Linux, and some websites don’t want you using them unless you’re on Windows or Mac.