As a workaround, you may use whatever reachable URL as an OAuth redirect URL and use webRequest.onBeforeRedirect - https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest/onBeforeRedirect to capture the redirect attempt and 'force redirect' e.g. by tabs.update - https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs/update. Although this will work, it is far from being elegant. It could even be error-prone. While Firefox offers a decent solution for this, why safari can't / doesn't. So, if it is an intention for Safari not to support this workflow, I would like to submit my post as a change request because this is so common usecase. (or please suggest where I can submit a change request for this???)

This problem seems to be resolved in Safari Version 15.4 (17613.1.17.1.6).

I have experienced a similar issue where a number of web extensions stop working on Safari 15.4. A deeper investigation shows that this is likely a Safari issue in breaking the web extension 'tabs' API: chrome.tabs.create doesn't work when the url is a page that's packaged with an extension. It seems to crash and ruin all chrome.tabs event handlers. Reproducible scenario: chrome.tabs.onActivated.addListener(()=> console.log('new active tab')) .. Note: I use onActivated just to test whether event listeners on tabs still works. Switching between tabs.. You should see the 'new active tab' printed in the console. chrome.tabs.create({url: chrome.runtime.getURL('/index.html')}) --> a new tab is created. Note: index.html is an html file packaged in your extension. Switching between tabs.. Expect: 'new active tab' printed in the console as usual Actual: no 'new active tab' printed in the console… Note: this problem does not occur when the url is a public reachable URL, nor on Safari 15.3 Version 15.4 (17613.1.17.1.13) Please fix.

for @rtolton, this is an example code: 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. } })

Safari Web Extension does not fully implement the web extension APIs -- some implementation details deviate from the spec e.g. no runtime.onMessageExternal https://developer.apple.com/forums/thread/681378 difficult to implement an OAuth flow due to no reachable extension-specific URL https://developer.apple.com/forums/thread/670165 Safari-specific implementation of runtime.sendNativeMessage And APIs get broken from time to time e.g. : storage.local.get behaves unexpectedly on Safari 18 https://developer.apple.com/forums/thread/765169 same for tabs.onRemoved on Safari 18 https://developer.apple.com/forums/thread/765343 Collectively, this makes it very difficult to develop JS web extensions for Safari.

storage.managed is not supported in Safari as also stated in MDN.

Whatever best practice materials you found on Firefox / Chrome are mostly applicable for Safari Web Extension too as they share the similar APIs.

Fixed in Safari 18.0.1