Hello @qbey,
Thanks for using the Yoast SEO plugin. Sadly, I was not able to replicate what you described with WordPress 6.4.1, Yoast SEO 21.5 and Classic Editor 1.6.3 on Mozilla Firefox 118.0.2 (32-bit). The Yoast SEO meta box shows as expected. See screenshot.
Thread Starter
qbey
(@qbey)
Firefox 91.1.0esr (64-bit) is installed here.
From here, I see the latest version of Mozilla Firefox is v119.0.1. I suggest updating your browser to that version. If you are unable to do so, please use Google Chrome since you mentioned there were no issues experienced with it.