Contentscripts are not executed for frames within extension popups even with all_frames set to true. Sample extension: https://github.com/carlosjeurissen/webext-tech-demo-extensions/tree/main/issues/safari-9637605-all-frames-in-content-script-popup In Google Chrome, the frame will turn red. In Safari nothing will happen.
Previously reported as: https://feedbackassistant.apple.com/feedback/9637605 https://developer.apple.com/forums/thread/690341
rdar://83279955