I think i found the answer that will work for you, open the quicktime control panel - browser tab - and hit the MIME settings button. This appears to be the list of programs the quicktime plugin opens from your browser. The "file types" tab in the control panel seems to only control what opens when you would double click on items in Windows itself.
So two places to control file types - mime settings and the "file types" tab. This (in my opionon) is very confusing and a design flaw, but it is at least fixable.