No reply necessary: starting yesterday, all of my extensions (Firefox Containers, Newsguard) are listed as outdated and to be replaced. Going to the Firefox Containers download page and clicking the download link signals an error about a download failure. Looks like this could be related to a change to how extensions are applied (or not) in private windows.

I (appear to have) solved this by just starting up with a fresh profile in Firefox, not a huge deal, but this may affect others as well...