At some point, I've noticed that certain behaviours expected to occur when pressing the Escape key no longer did. Those behaviours mainly involved triggering some Javascript, including functionality in keyboard-related extensions, such as Tridactyl. Browser-level functionality on the other hand, such as pressing Shift-Escape to open `about:processes`, or pressing Escape to close Search Suggestions when the URL input bar, continue to work as before. Upon investigation, I found it is specifically the javascript Keydown event that isn't being registered, while the subsequent Keyup event still is. I used https://w3c.github.io/uievents/tools/key-event-viewer.html to test this. I also found that starting Firefox in Troubleshoot Mode (Safe mode) doesn't resolve the issue. On the other hand, creating a new profile does. I've looked at the modified settings in `about:config`; there's a lot, but nothing stands out as being related to keyboard input or javascript. Can someone please help me find what is causing this?