ImNotRen if you want to integrate Google Analytics, use the "FoF Analytics" extension. FreeFlarum does not support full Google verification yet, but it might in the future. I think that it's because Google requires the code to be placed in the header, in the <head>
tag, and that seems to not work well on FF, despite the code being indeed placed in the head. I'm not sure why it works like this, and I might look into it in the future. But that's why we have that extension installed, and you usually don't need to use the verification for any other purpose than Analytics.