« Safari 12 can only run Safari App Extensions,1) a much more limited type of extension that must be distributed as part of a Mac app in the Mac App Store. Whereas the previous Zotero Connector for Safari shared a large amount of code with the Zotero Connectors for Chrome and Firefox, creating a Safari App Extension would require a near-complete rewrite of the extension, all to produce a much less featureful extension…
To continue using Zotero with Safari 12, install the Zotero Bookmarklet. The bookmarklet will allow you to save items to your online library, and Zotero will then sync those items down to your computer. We'll soon be releasing an updated version of the Zotero Bookmarklet that will allow you to save directly to Zotero on your computer without relying on syncing, along with other improvements. With this updated bookmarklet, we hope to offer most of the functionality that would be possible in a new Safari extension… ».