The only explanation I can come up with is that you accidentally clicked on disable -- there's no confirmation dialog for that. The versions are all OK.
I don't believe so. FF came up with a yellow bar saying some of my extensions would be disabled or are disabled. I clicked "Learn More" and the add-ons page came up in a new tab. To my surprise it said that Zotero would be disabled at next restart and that there were 2 other add-ons already disabled.
Zotero 4.0.29.10
The zotero ad-on now says it will be reenabled on restart. But it didn't update.