Running Mozilla Firefox, version 50.1.0, under Ubuntu 16.04, a 2 weeks fresh install. Whenever I try to bookmark a page, I press CTRL+D to open the "Page Bookmarked" dialog. Upon editing any of the fields, the very first key I hit causes the dialog to close, in effect not allowing me to change e.g. the Name, Folder or Tags. What I notice is that the page did get bookmarked (with the default settings for those fields). I also notice that the key I hit seemingly not just closes the dialog, but is also transferred to the currently active web page. E.g. when I bookmark this page, the keystroke is transferred to this textbox (also happens on pages where I'm not filling in a form). I have already: * restarted with add-ons disabled * refreshed firefox * removed the contents of $HOME/.mozilla/firefox None of which worked. I am not afraid to loose current settings, like I said this is a fairly new installation and I haven't made that many changes yet. The Ubuntu Modifications add-on is currently the only add-on left. Disabling it (& restarting firefox with that add-on disabled, for good measure) also does not solve the problem.