Since the challenges are already limited to a single weapon, it is very annoying to have to click twice to engage the weapon. Please consider activating the weapon immediately after clicking the weapon button rather than popping up the single-weapon weapon select dialog.

You can re-activate the weapon you used in the previous turn by clicking the movement button, which should save you a bit of time :)

Also, initially, if there is only one weapon available the movement button will toggle selection of that (if there's more than one it will select the first one in the list)

I think it's a bit of an anti-pattern to expect users to know to "deactivate" the movement button in order to quickly access their weapon. If I see a weapon button, it is fair to assume that is what should be clicked to access the weapons.

Movement and using a weapon are mutually-exclusive states. Wouldn't it make more sense to have these behave as radio buttons? In that pattern, there is no "deactivate" case but only changing your selection between the two states.

In the Challenges, the game forces the player out of Firing mode and back to Movement mode after taking a shot (assuming they now might want to walk), but it doesn't have to - it's just a case of picking one or the other (there's no best way, as it depends on what you might want to do next).

With the current control scheme (and Flash limiting the available keyboard controls in full screen mode) we don't have a combined Movement & Firing mode.

It's a good point about the Firing/Movement buttons and states (and in particular, the obsolete step of selecting the only available weapon when in single-weapon challenges). We'll consider a clearer way to handle this :)