Selenium moving to absolute positions
The problem in my case was that I was not waiting for the element to load. At least I assume that's what the problem is because if I allow selenium to wait for the element instead and then click on it, it works.
I'm using the python package to move the mouse in some specified pattern or just random motions. 
The first thing I tried is to get the size of the //html element and use that to make the boundaries for mouse movement. However, when I do this the MoveTargetOutOfBoundsException rears its head and displays some "given" coordinates (which were not anywhere near the input.
The code I used:

origin = driver.find_element_by_xpath('//html')
bounds = origin.size
print bounds
ActionChains(driver).move_to_element(origin).move_by_offset(bounds['width'] - 10, bounds['height'] - 10).perform()

So I subtract 10 from each boundary to test it and move to that position (apparently the move_to_element_by_offset method is dodgy). 
MoveTargetOutOfBoundsException: Message: Given coordinates (1919, 2766) are outside the document. Error: MoveTargetOutOfBoundsError: The target scroll location (17, 1798) is not on the page.
Stacktrace:
    at FirefoxDriver.prototype.mouseMoveTo (file://...
The actual given coordinates were (1903-10=1893, 969-10=989).
Any ideas?