Awesome news! I've been working very hard on getting Revert Site working again, & succeeded! The new version uses a different method to get the old site back than before and this time should have fewer side effects (video and audio calls should work ok for instance)
Disaster strikes for Revert Site. It looks like Facebook have closed the loophole that the Revert Site extension was using to get the old Facebook design back.
I will try and find a way around it, but this could be the end of the old design for us, unless you are a Page or Group admin, and have the option at the top left of the group/page itself to revert for 48 hours.