Unfortunate; This morning my firefox profile didn't start up, draws the empty window, and spins the CPU. I started my workday with downgrading FF and restoring my previous profile from a backup.

Now this.

FWIF, for this particular problem, the workaround from the linked reddit post works:

Edit 3: This workaround seems to fix it:

    type about:config in the URL bar
    search for network.http.accept-encoding.secure
    replace gzip, deflate, br, zstd with gzip, deflate, zstd

Alternatively, set network.http.dictionaries.enable to false.