The inputFile component is not working with FF 3.0.7.
The cause is that the "action" attribute of the upload form is set, via javascript, to a relative (web-context based) URL. Changing the URL to fully qualified fixes the problem.
It appears that Firefox 3.0.7 includes a change so that if you create dynamic contents to the iframe, then any form inside must use a fully qualified URL for the form action.
The following demos demonstrate the issue with Firefox 3.0.7

• This uses upload component markup in the page; it works fine
• This uses upload component inside an html file which is the iframe src; it works fine
• This generates upload contents of the iframe using javascript; it does not work