In Control Center>Edit IceWM Settings>'keys' tab:
I find that

key"F6" iceweasel

is not good because F6 is a default shortcut in Iceweasel (address bar) so maybe should be replaced by

key"F2" iceweasel

The default settings have a # preceding the keys definitions, you must remove the # then restart icewm in order to make those changes effective.

cheers,
oldhoghead

Thanks olghoghead, I edited the first post and the shortcuts are working ok. But I changed the shortcut for Iceweasel from F6 to F2, otherwise Iceweasel's address bar shortcut would be overridden.