% uname -a Linux phoebe 3.2.0-33-generic #52-Ubuntu SMP Thu Oct 18 16:29:15 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
I'm running 12.04 on the machine I'm typing this on, and I've been running it for quite some time. I just did a dist-upgrade, and it included some update for Firefox (to 17.0.1 now). After restarting the browser, I noted with some surprise that I can't type back-quotes or tildes. They worked just a few minutes ago before the update, but not now.
I use a Deck keyboad, and I have the back-quote/tilde key remapped. I've had the keyboard for many years now and the remapping has always worked:
% xmodmap -pk | egrep tilde 133 0x0060 (grave) 0x007e (asciitilde) 0x0060 (grave) 0x007e (asciitilde)
I can type those characters into xterm windows, into Chrome, gvim, gedit, etc. What in the world is going on with Firefox? I can't find any relevant configuration options, and I certainly haven't been tinkering with them. I've tried restarting it a couple times too.
I'll try running a new clean profile and see if that makes a difference; I do have some add-ons but nothing new and nothing particularly crazy. edit Nope, can't type the characters in a plain-jane profile either.
edit — reinstalled Firefox, same thing.
edit again — I've also found that VirtualBox seems to ignore the xmodmap remapping. I've basically got the grave/tilde key swapped with another key that's remapped to "Alt". In VirtualBox now (I don't think it was always this way, but I'm not 100% sure), I can type back-quote or tilde with the key that's swapped to "Alt". However, that does not work in Firefox — neither key works as the grave/tilde key, though I've just verified that the remapped "Alt" key in Firefox does work (as "Alt")!!
edit yet again — upgraded to 12.10, same problem. Something changed somewhere, as I am 100% positive that that key was working today and over the past many months. (Why? How do you quote code snippets inline in Markdown? I'm on Stackoverflow a lot and that's how I noticed it was broken.)