Mozilla's engineers say the risk is limited to a denial-of-service issue. From the article: "'As part of our talk we mentioned that there was a previously known Firefox vulnerability that could result in a stack overflow ending up in remote code execution. However, the code we presented did not in fact do this, and I personally have not gotten it to result in code execution, nor do I know of anyone who has... I have not succeeded in making this code do anything more than cause a crash and eat up system resources, and I certainly haven't used it to take over anyone else's computer and execute arbitrary code,' Spiegelmock said."
Spiegelmock also stated that the claim that there were 30 other undisclosed exploits was made solely by his co-presenter, Andrew Wbeelsoi.