UPDATED: as @papegaaij mentioned, the workaround to use webRequest.onBeforeRedirect does not work anymore in MV3. Anyway, you can use tabs.onUpdated instead. tabs.onUpdated provides changeInfo object where you can observe a url being redirected to. browser.tabs.onUpdated.addListener((tabId, changeInfo, tab) => { if (changeInfo.url && changeInfo.url === 'your-reachable-redirect-url') { // do your post sign-in ceremony // e.g. take authCode from the query param, etc. } })

the workaround still works in MV3. Please see my updated comment above.

Thank you for your reply. Good to know you've a fix for it. When will it be available by the way? My web extension is suffered from it and currently being rejected from the Apple Review because of this bug. I have another bug to report related to tabs.onRemoved. Safari 18 throws tabs.onRemoved incorrectly when redirect to a different scheme e.g. from https to safari-extension. Where is the best place to report this issue? Here in this forum or WebKit repo on Git?

I am aware of the post regarding tabs.onReplaced. However, that does not address my issue. Unlike, tabs.onReplaced, the Safari-18-specific tabs.onRemoved behaviour cannot occur in Chrome or any browsers under any conditions. It's clear that tabs.onRemoved shall be fired when a tab is closed. According to my scenario, no tab was closed. I disagree that this is an expected behaviour. Please help.

@ItsMika thanks for your answer. I wonder if this solution still works on an MV3 web extension as a background script is no longer there.