After creating some simple button states and going to preview in File/Rune Project I get nothing but hang in Firefox 3.53. Flash 10's installed etc but the page hangs with "waiting for fpdownload.adobe.com. It worked - really slowly - the first couple of times I tried previewing experiments but now it sends Firefox into "not responding" mode.
I've sometimes seen this when I have a limited internet connection. Is your internet connection fully functional and reasonably high-speed?