frag.jetzt unusable with private window in Firefox 107

[lechten]

With a private window in Firefox 107.0 and 107.0.1 under GNU/Linux and Windows, frag.jetzt is unusable. The page loads but is dark grey. Some black icons are barely visible at the bottom, but the usual Welcome message with Onboarding button is not visible.
This is particularly bad if students want to enter a room in a private window.

The browser's console shows errors:

ERROR Error: Uncaught (in promise): IndexedDB error: InvalidStateError: A mutation operation was attempted on a database that did not allow mutations.
    Me https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    Me https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    Ie https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    onInvokeTask https://frag.jetzt/main.596646befc1b5201.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    runTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    B https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    le https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    oe https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    Ne https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
ERROR TypeError: this.room is null
    announce https://frag.jetzt/9018.ae461437ba85fe43.js:1
    listenerFn https://frag.jetzt/9018.ae461437ba85fe43.js:1
    J https://frag.jetzt/main.596646befc1b5201.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    onInvokeTask https://frag.jetzt/main.596646befc1b5201.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    runTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    invokeTask https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    le https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    oe https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1
    Ne https://frag.jetzt/polyfills.8c46eac9e9708b77.js:1