A little bit of research on Browser support for functions keys. The keys marked with OK are available to programmers, the rest is dedicated to the browser specific functionality.

OK - is available

N/A - not available

IE 9+:

F1 – **onkeydown: **OK, **onkeyup: **N/A (opens IE Help file in a new window)

F2 – **onkeydown: **OK, **onkeyup: **OK

F3 – **onkeydown: **OK, **onkeyup: **N/A (opens search box)

F4 – **onkeydown: **OK, **onkeyup: **N/A (opens url history)

F5 – **onkeydown: **N/A (refreshes the screen), **onkeyup: **OK

F6 – **onkeydown: **OK, **onkeyup: **N/A

F7 – **onkeydown: **OK, **onkeyup: **N/A (opens Caret browsing dialog)

F8 – **onkeydown: **OK, **onkeyup: **OK

F9 – **onkeydown: **OK, **onkeyup: **OK

F10 – **onkeydown: **OK, **onkeyup: **OK (+ enables/disables top task bar)

F11 – **onkeydown: **OK, **onkeyup: **OK (enables/disables full screen)

F12 – **onkeydown: **OK, **onkeyup: **N/A (enables/disables Inspect Element screen)

Chrome 33.0:

F1 – **onkeydown: **OK, **onkeyup: **N/A (opens Chrome Help file in a new tab)

F2 – **onkeydown: **OK, **onkeyup: **OK

F3 – **onkeydown: **OK, **onkeyup: **N/A (opens search box)

F4 – **onkeydown: **OK, **onkeyup: **OK

F5 – **onkeydown: **OK, **onkeyup: **OK (refreshes the screen)

F6 – **onkeydown: **OK, **onkeyup: **N/A

F7 – **onkeydown: **OK, **onkeyup: **OK

F8 – **onkeydown: **OK, **onkeyup: **OK

F9 – **onkeydown: **OK, **onkeyup: **OK

F10 – **onkeydown: **OK, **onkeyup: **OK (second press only – enables/disables full screen)

F11 – **onkeydown: **OK, **onkeyup: **OK (enables/disables full screen)

F12 – **onkeydown: **OK, **onkeyup: **N/A (second press only – enables/disables Inspect Element screen)

Firefox 19.0:

F1 – **onkeydown: **OK, **onkeyup: **OK

F2 – **onkeydown: **OK, **onkeyup: **OK

F3 – **onkeydown: **OK, **onkeyup: **OK (opens search box)

F4 – **onkeydown: **OK, **onkeyup: **OK

F5 – **onkeydown: **N/A, **onkeyup: **OK (refreshes the screen)

F6 – **onkeydown: **OK, **onkeyup: **N/A

F7 – **onkeydown: **OK, **onkeyup: **OK (+ opens Caret browsing dialog)

F8 – **onkeydown: **OK, **onkeyup: **OK

F9 – **onkeydown: **OK, **onkeyup: **OK

F10 – **onkeydown: **OK, **onkeyup: **N/A (second press only – enables/disables top task bar)

F11 – **onkeydown: **OK, **onkeyup: **OK

F12 – **onkeydown: **OK, **onkeyup: **OK