According to Wladimir Palant, FullerScreen extension messes the (S5) slides up badly.

No. Sorry Wladimir, but the fault is in S5's hands. Blame Eric Meyer :-) S5 links the document to a stylesheet for media="projection" that applies rules made only for OperaShow... In other terms, S5 contains an ugly hack for OperaShow. Any other browser implementing the projection medium will then suck on S5 in projection mode... Remove the corresponding link from your file and you'll see fullerscreen behave nicely with S5 (it might require to click twice on the Ø symbol to let S5's code reflow everything).