It's sad how Mozilla killed Vimperator with the transition to WebExtensions. And how many of its features still cannot be replicated in Tridactyl, which I otherwise love, despite all your efforts.

Due to the new addon model, addons don't get the chance to run till the page finishes loading. So e.g. a 404 or a slow page force you to revert to standard keybindings which ruins the immersive Vim user experience.

Mozilla should perhaps create an API for privileged extensions. I know the userbase is small. But it's a very important userbase to keep the platform healthy.