Why Are Extensions Incompatible with Safari in macOS 13?

Users upgrading to or using macOS 13 (Ventura) often discover that several browser extensions either fail to install, stop working, or disappear entirely from Safari. This incompatibility stems primarily from Apple's strict transition to the modern WebExtensions API, the absolute phasing out of legacy extension architectures, heightened security and notarization requirements in macOS Ventura, and differences in how Safari handles extension permissions compared to other browsers.

Phasing Out of Legacy Safari Extensions

In recent years, Apple systematically phased out traditional extension formats. Legacy Safari extensions (typically ending in .safariextz) used an older, proprietary architecture that granted extensions deep, broad access to the browser. Starting before macOS 13 and fully enforced in modern Safari releases, Apple completely eliminated runtime support for these legacy formats. Any extension that has not been converted to the current standard cannot run on macOS 13.

The Safari WebExtension Architecture

Safari 14 and later versions, including Safari 16 on macOS 13, rely on the cross-browser WebExtensions standard. However, unlike Google Chrome or Mozilla Firefox—which allow users to install standalone extension files directly from web stores—Apple requires Safari extensions to be bundled inside a native macOS application. If a developer has not packaged their code inside a native container and adapted it using Xcode’s conversion tools, the extension cannot function in Safari.

Strict App Store and Notarization Requirements

macOS 13 enforces strict gatekeeping, sandboxing, and code-signing rules. To run on macOS 13, a Safari extension must be:

  • Built within a native app wrapper.
  • Signed with a valid Apple Developer certificate.
  • Distributed either through the official Mac App Store or notarized by Apple to bypass Gatekeeper security.

Extensions from unverified sources or independent developers who have not paid for an Apple Developer account are blocked by the operating system’s security layer.

WebExtension API Discrepancies

While Safari supports the WebExtensions standard, its implementation is not identical to Chromium. Safari enforces strict privacy-focused limitations on certain APIs, particularly those involving background processing, persistent web requests, and ad-blocking mechanisms. For instance, Safari heavily favors its native Content Blocking API over resource-heavy webRequest APIs used by traditional blockers. Extensions that rely on Chromium-specific APIs without custom modifications for WebKit will fail to load or behave erratically in Safari 16 on macOS 13.

Developer Maintenance Costs

Because packaging an extension for Safari requires a Mac, an active Apple Developer Program membership ($99/year), and dedicated maintenance to comply with Safari’s unique sandboxing rules, many open-source and independent developers choose not to support Safari. Consequently, extensions that thrive on Chrome or Firefox frequently remain unavailable or outdated for Safari on macOS 13.