When I open the analysis board for a game and click on the little book icon for the opening explorer, I get an "Oops, sorry!" error message displayed in the opening explorer tab. When mousing over it, an additional error is displayed: "The explorer is temporarily out of service. Try again soon!". This only happens in Firefox.
Try restarting your internet connection and then going back to it. This has only happened to me before when I had a bad connection that disconnected before connecting to the opening explorer.
It's working fine for me on firefox right now.
This can happen if you have a script blocker or similar that blocks the lichess.ovh domain.
Yes, that was it! Thank you, cyanfish.
I'm using NoScript, but the add-on wasn't reporting lichess.ovh as one of the participating domains. Once I added it to the exception list by hand, it worked.
