The double ;; is not really a problem (although I have notified the developers and the extra ; characters should hopefully be removed in the next version of Juicebox). The ; character is used to separate CSS rules and, although there is nothing between the two ; characters, the code is still technically valid and will not cause any problems.
The most likely reasons for seeing a blank page on a mobile device are either:
(1) JavaScript is disabled in the browser.
... or:
(2) The gallery is being displayed over a 3G connection rather than wi-fi.
Please check that JavaScript is enabled and if 3G is being used, please see this FAQ which has a solution to the problem.
Why can't I view my gallery on a 3G mobile connection?
(not tested on a Windows PC)
Your gallery displays and functions fine on a Windows PC.