So today I learned that it actually is possible to change the keyboard behavior in Linux in such a way as to allow Ctrl+Alt+F1 to toggle the viewer UI in Linux. For a long time, I thought it was hard coded, that there was no way to stop the OS from trapping the shortcut, even if there was a way to stop it from switching to a PTY. But there is, and every flavor of Linux I've tested (a few Debian-based, a few RPM-based and one from scratch) includes some X keyboard tools, one of which we can use to disable the capture of Ctrl+Alt+F1 - setxkbmap.
It's a CLI command, no GUI used, though some desktops, like Unity and KDE, do have a GUI control panel you can use to get to the same function. I'm not going to describe all the possible GUI methods, instead I'm going to show you how to use the command in the Terminal. It's too simple to be burdened by a GUI.
Open a terminal (Ctrl+Alt+T in most Linux versions), then type:
setxkbmap -option srvrkeys:noneand press Enter. And from then on, you can press Ctrl+Alt+F1 and it will work in any program that wants it. To unset that, use:
setxkbmap -optionand press Enter.
A caveat to this option is that it affects all key combos that the X server would normally trap, like Ctrl+Alt+Backspace, so if you need the shortcuts normally, you want to unset the option when you're done. One way to do that would be to add those two commands to your firestorm script, setting the option before invoking the viewer and then unsetting near the end.
A warning: if you already have other options enabled, and you add srvrkeys:none, there isn't a way to unset a single option. You would have to script up a function that copies the current option set, adds srvrkeys:none, then restore the original option set when done. I expect I'll try to make that work, and if I do I'll publish the script here