Heyo
If a guest tries to search the forum and the google captcha is enabled, no matter if it is solved or not, the error "Please enter the verification code below to continue to the results." will appear and prevent the guest from performing a search.
As far as I know, the same issue happens when a regular member tries to preview a post when solving the captcha, however, if they hit "Post" instead of "Preview", no errors and the post is successfully made.
Can anyone else confirm? Latest github version btw.
I can confirm a little-your first paragraph-, that with the "new", Firefox [Not sure about Chrome], it has a looping Google Captcha with -many- websites [in general/ not necessarily smf related].
For your second paragraph. I really wouldn't know.