Thomas Mulhall wrote:

Hi which extensions did you update and which extensions is causing this problem. And no extension.json should be included so the file may be missing from extension.

The extensions in question are "YouTube" and "MobileFrontend". Just downloaded both of them (along with MediaWiki) this week, so they should theoretically be current.

I've since replaced my YouTube attempt with EmbedVideo instead, so that one is more academic at this point.

However, MobileFrontend is the one I'd REALLY like to get working.