Safari Extension Error: “Non-persistent background content cannot listen to webRequest events.” after macOS 15.4 / Safari 18.4 Update We’re seeing the following error in the Safari Extensions tab after updating to macOS 15.4 and Safari 18.4: “Non-persistent background content cannot listen to webRequest events.” This error did not appear prior to the update, and we haven’t found any official documentation stating that webRequest API is no longer supported in Safari. In our extension (Manifest V3), we are using the webRequest.onHeadersReceived callback to intercept response headers and read updated cookies. While the functionality itself still works as expected. we’re able to access the response headers and this error is now shown in the Extension settings page. We are not seeing this issue in other browsers (Chrome, Firefox) using the same Manifest V3 setup. Is there any plan to deprecate webRequest support in Manifest V3 for Safari? We’d appreciate any clarification or guidance on how to handle this going forward.

We’re seeing an issue in our Safari Web Extension where not all cookies from the Set-Cookie response header are accessible. We are using macOS 15.4 and Safari 18.4. In the webRequest.onHeadersReceived callback, the Set-Cookie header returned by Safari only includes some of the cookies set by the server. If multiple Set-Cookie headers are present, we seem to receive only a partial list, some cookies are missing entirely. In Chrome and Firefox, the same callback provides all cookies set by the server without issue. We are looking for assistance in fixing these issues and having our Safari Extension function the same as it does in Firefox and Chrome.

We’re encountering an issue when trying to add non-standard headers to outgoing requests using Declarative Net Request (DNR) rules in our Safari Web Extension. Tested on macOS 15.4 with Safari 18.4. Specifically, when attempting to add a custom header such as "X-Custom-Header" using a DNR rule, the header does not appear in the request. We are able to add standard headers like "Authorization" and "Cookie" to the request successfully using the same method. This behavior suggests that Safari may be filtering or blocking non-standard headers when set via DNR rules, unlike other browsers. In Chrome and Firefox, the same rule adds the "X-Custom-Header" header without any issue. We are looking for assistance in fixing these issues and having our Safari Extension function the same as it does in Firefox and Chrome.

When a DNR rule is set for a specific URL and the request receives a server-side redirect (e.g., 302) to a different URL that does not match the urlFilter, the rule still seems to apply to the redirected request. We are using macOS 15.4 and Safari 18.4. For example, consider two sequential calls: call1 and call2. call1 triggers a 302 redirect to call2. A DNR rule is created to add a "Cookie" header to call1 based on its URL. Unexpectedly, the same cookie is also added to call2, even though call2's URL does not match the rule's urlFilter. This results in the Set-Cookie response from call1 being ignored, and call2 receiving the manually set cookie instead—leading to incorrect behavior. This issue doesn't occur in Chrome or Firefox, where the rule is not applied to the redirected request if the URL no longer matches. We are looking for assistance in fixing these issues and having our Safari Extension function the same as it does in Firefox and Chrome.