Something the article doesn't mention (
source):
1 - Accuvant was paid by Google itself to do the study. It does not necessarily mean that Accuvant cheated. They exposed their methodology and it seemed legit
2- However it based the results on a technique called "sandboxing" that Chrome implements and IE does a bit, but Firefox is very new to it.
Mozilla replied by saying that "sandboxing" is only one of the techniques used by FF for security. They haven't implemented it correctly, but it's not the only existing security measure.
Bottom line, I don't believe FF is less "secure" than any other browser, just that it implements security differently.