Hello - we have a Mac application that uses a browser extension and the web extension JS APIs to communicate with Safari. As of macOS 15.4 / Safari 18.4 the tab OnAttached and tab onDetached events are no longer received. After some testing we verified that the events were working properly as of macOS 15.3 / Safari 18.3 but appear to have been broken in macOS 15.4. Note a similar issue was reported previously for Safari 17.6 and was fixed in macOS 15.0 (FB14324177). We have made a TestFlight version of our app (Tabby) available to simplify debugging via https://testflight.apple.com/join/Va8Zdv9d. To reproduce the issue: Install the Tabby TestFlight build on macOS 15.4 or 15.4.1 Open Safari, go to Safari settings and select the Extensions tab Enable the Tabby extension and grant permissions to all windows all the time Open a Safari window with at least 3 tabs Note the open window and tabs displayed in Tabby In Safari, perform a tab detach by dragging a tab out of the window Expected behavior Within Safari the detached tab should now be in it’s own window, and via the onDetached event Tabby should update to show the tab in it’s own window AND removed from the original window. Observed Safari fails to send the onDetached event and Tabby will continue to display the detached tab in its original window in addition to the new window. You can also use the repro steps above to observe the onDetached event being received or not by Tabby in the Safari developer console. The same steps but re-attaching the tab to the original window can be used to observe the onAttached event being received or not. We’ve attached two screen recordings to the Feedback ID below, one showing the events working on macOS 15.3, and one showing the events failing to be received on macOS 15.4.1. Note it also fails on macOS 15.4. FEEDBACK ID: FB17367977

Hello - we have a Mac application that uses a browser extension and the web extension JS APIs to communicate with Safari. During user testing we found that the tab title and tab URL properties are empty when obtaining the set of open windows via windows.get() after a Safari restart. We are testing with Safari 18.4 (20621.1.15.11.10). We have made a TestFlight version of our app and extension available to help with testing: https://testflight.apple.com/join/Va8Zdv9d. Screenshot and screen recording are attached to the Feedback ID supplied below. STEPS TO REPRODUCE Install Tabby via the TestFlight link Enable the Tabby for Safari extension in the Safari extensions dialog Grant permissions for Tabby for Safari to all windows all the time Within Safari, open two windows each with at least two tabs Within the Tabby app, ensure you see the windows and tabs listed correctly (tab title displayed for each) Quit and restart Safari Expected behavior Safari re-opens existing windows and Tabby displays title for each tab Observed Safari re-opens existing windows but within Tabby all tabs except the current tab are displayed with a title of “Start Page”. Under the hood the tab title and tab URL properties are empty when returned via a windows.get() call after Safari restarts. NAME AND APPLE ID OF APP Tabby - Browser Tab Manager 1586203406 FEEDBACK ASSISTANT ID FB16389506