Can you open an issue upstream at https://github.com/jlebon/textern and we'll debug there? I'd like to help you but it's painful through this interface. Also check out previously closed issues for debugging steps, e.g. https://github.com/jlebon/textern/issues/4 and https://github.com/jlebon/textern/issues/7. Re. Ctrl+Shift+E, odd I hadn't noticed that before. I wonder if it's new in the latest version of Firefox. Regardless, feel free to change the mapping in the editor settings to something else if you'd like.