Unable to log in to plex.tv

I am trying to sign in to plex.tv in the hopes of downloading the media server. I get the front page of the site OK, but when I try to use the “Sign In” menu item, it just shows me the “Account Sign In” white box and a spinning graphic. This is in all web browsers I have installed. This is on a Linux box. In Firefox, there are Javascript errors. Among them:

Load denied by X-Frame-Options: https://app.plex.tv/auth-form/#!?enableSignInWithApple=1&skipLanding=1&signUp=0&forwardUrl=https%3A%2F%2Fwww.plex.tv%2F%3FsignUp%3D0&externalFederatedAuthCompleteUrl=https%3A%2F%2Fwww.plex.tv%2F%3FsignUp%3D0&clientID=8dba262b-b223-5231-742f-4ff9e922fa97&context[device][product]=Plex%20SSO&redirect_uri=&provider=&state=&id_token=&code=&externalFederatedAuthComplete= does not permit cross-origin framing.

How am I supposed to be able to sign in to the site?