Disable Esc shortcut to quit Fullscreen

it is way easier - in firefox

1. in the url bar write "about:config"
2. agree with security risks
3. search for "escape", it should find the entry "browser.fullscreen.exit_on_escape"
4. doulbe click on "true", it should go to "false"

you´re done - enjoy :-)

Good question. Before browser makers figured out cmd-q was awfully dangerous without at least a prompt that the user really wants to close 60 tabs, I always changed the keyboard shortcut for the Quit command on my main browser. You can disable shortcuts via Keyboard Shortcuts.

1. Open System Preferences: Keyboard.
2. Click Keyboard Shortcuts in the top pill shaped tab.
3. Click the Applications Shortcuts icon in the left hand column.
4. Choose Safari from the drop down menu of offered applications (looks like the default list is applications which have been opened in the last three months).
5. Enter the exact name of the menu item you wish to disable. In this case "Exit Full Screen".
6. Add an alternative keyboard shortcut (in this illustration, I added Ctrl-Opt-Cmd-c) This is what the finished result looks like.
7. Test (alternative Application Shortcuts do now always work exactly as planned).

You can do the same thing with Keyboard Maestro (and much much more). Apple's feature is probably taken/adopted from Peter N. Lewis's implementation (which existed for many years before Apple came up with the feature in Snow Leopard). In Keyboard Maestro, you can also assign the same shortcut to multiple applications. In Keyboard Maestro, you can also take over keyboard commands which do not have menu items (complex applications like Photoshop come to mind: there are so many commands that many of the commands have no menu equivalent). It's also easier to move these preferences around from computer to computer if you are using Keyboard Maestro.

On the other hand the Apple version exists on all Macs past 10.6.8, including your less technical girlfriend's MacBook Pro. I use both depending on whether I want a quick fix or if I'm building permanent tools/shortcuts for an application I use professionally on multiple computers. Keyboard Maestro does far more than just substitute keyboard shortcuts: you can write sequential macros with pauses to automate what would otherwise be five or ten keypress and click type actions, i.e. redirecting, address and send email to someone else in the company with a single keyboard command.

Oh, finally I did it!

Using Better Touch Tool app (but I think other such apps might work as well).
Added a custom keyboard shortcut ⎋Escape for Final Cut Pro which does nothing.

As a drawback, you won't be able to do useful things with Escape key (i.e. closing Preferences window).