[cm3]

Have you tried using Vivaldi? It's awfully slow to respond to user interaction because it's all HTML. Say what you want about XUL, but for something aiming to be like HTML it never felt slow. If Vivaldi's non-existing responsiveness is what the new Firefox will be, then they should seriously consider to rewrite the whole thing like a game (in OpenGL/Vulkan) instead. Oh and XUL was optimized for memory efficiency, which will have to be reoptimized for the HTML-only interface, but that can benefit the whole web.

[angry-hacker]

Vivaldi is much faster than Firefox on both Linux and Windows, where I'm using it. Of course it's still alpha software, but the UI is blazing fast compared to FF.

[cm3]

It's substantially slower than Chromium and Firefox for me on Linux. Both Chromium and Firefox are very fast in comparison on my machines. I'm glad it's faster for you, I really am.