Google reCAPTCHA with Firefox Focus on iOS
If you have Firefox Focus installed and enabled on iOS then Google reCAPTCHA challenges are filtered out. Depending on the site configuration you’ll likely see an error after submitting a form and wonder what is going on, because you never saw the challenge.
The only solution I know of right now is to change the default settings in Firefox Focus.
Start Firefox Focus and go to the settings, by tapping on the gear icon in the top right.
Then deselect the “other content trackers”. Not sure what Google injects that makes Focus regard this as a tracking tool but that is the option you’ll need to disable. This isn't enabled by default, by the way.
With that disabled, the reCAPTCHA challenge will show.