Movement works fine (using the arrow keys) until after the button is pressed then movement no longer works.
Firefox (13.0.1), WindowsXP, Construct 2 (R95).
Do not know how to attach file so I uploaded example to internet (http://www.bluefiregames.com/test.zip).
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I see. Though there's no bug in Chrome.
But in Firefox, after clicking button, you should click in game window again, or else browser sets game window out of focus, and keys are in control of main window (arrows will scroll page instead of moving an objects ingame).
Bug confirmed for me.
I don't think this is a bug, as NugMan says Firefox just decides to transfer keyboard focus to the button instead of the game. To switch back you just have to click in the canvas. It doesn't happen in Chrome, but the behavior in Firefox is probably a reason to use sprites instead of button objects.