If your app is 3-6x slower overall in Firefox to the point of animations & dragging being slower, and to the point that non-minification makes it slower... some

If your app is 3-6x slower overall in Firefox to the point of animations & dragging being slower, and to the point that non-minification makes it slower... something is wrong with your app. Animations are generally the work of the layout engine and compositor, which is absolutely not going to be impacted by jsc's latest JS optimizations, or by ES6 features. For one thing, minification's impact is largely on parsing, so it shouldn't have any noticeable impact on anything other than startup time and memory usage (the compressed JS source for Function.toString will be a bit smaller if minified). If your app is really slower at runtime when not minified, again, something is wrong. Is your application written in raw (non-transpiled) ES6 and heavily using generators, async, tail call opts etc in tight perf-sensitive loops that run on the main thread without yielding to the event loop? It's hard for me to come up with a scenario where you could see such a huge performance gap in a well-constructed application. If computational performance is really important to you, then you're writing asm.js (or webassembly) and shipping that. All of the modern JS engines perform great on that sort of code and you simply cannot see a 3-6x gap there. So something weird is going on with your app that any vendor would be happy to fix if you sent them a repro (or just let them try out your app).