The tutorial was quite excellent. Unfortunately I get stuck at the "zooming" portion. Pressing ctrl+[ does nothing for me. (Firefox 32.0 on Ubuntu 12.04)
Or it might be that in my keyboard layout, [ and ] requires pressing RIGHT ALT + 8 and RIGHT ALT + 9, respectively.
[1] https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perf...
PS: Indeed changing the layout to en-US fixes the problem, but that not a real solution.