OSX 10.6.8
Firefox 13.0.1
When I select the drawing tool and then shift-drag to draw a line conforming to the grid, the when I let go of the mouse button Firefox opens a new browser window titled "Mozilla Firefox" and a dialogue box pops up telling me that I have asked to open original.gif, a 1.0 MB document from <a href="http://files.d20.io" rel="nofollow">http://files.d20.io</a> , and asking me what to do with it.
