The Zotero Connector for Safari is bundled with the Zotero desktop app. (Current versions of Safari don't allow direct installation of browser extensions like other browsers.) After opening Zotero for the first time, you can enable the Zotero Connector from the Extensions pane of the Safari settings (“Safari” menu → “Settings” → “Extensions”, not “Safari” menu → “Safari Extensions…”).
The Zotero Connector for Safari requires macOS 11 Big Sur or later.
Using an iPhone or iPad? You can save to the Zotero iOS app using the Share sheet in Safari and other browsers.
If you find that the extension has disappeared from the Safari toolbar or is quickly appearing and reappearing, try closing Safari, deleting the Zotero app from Applications, and redownloading Zotero from the download page. (Your Zotero data won't be affected.) It may also help to restart your computer in between deleting the app and redownloading.
We believe the potential causes of this problem have been fixed in Zotero 7. If you continue to experience this, let us know in the Zotero Forums. In the meantime, you may want to consider switching to a browser with a more stable extension framework, such as Firefox, Chrome, or Edge.
Due to technical limitations of the Safari extension framework, some features available in Firefox, Chrome, and Edge aren't available in Safari:
Other differences: