Code: Megapixel99/kestrel Kestrel is a macOS browser I have been building on WKWebView to test whether a browser can hold a memory budget the way a game engine holds a frame budget. It used to ship six built-in imitations of common extensions, including an ad blocker. When macOS 15.4 shipped WKWebExtension I replaced all six with the real thing: Kestrel unpacks an .xpi and hands it to WebKit, and all 25 add-ons from my Firefox profiles load. Then I measured whether the real ad bl...