Sigil edited epub doesn't want to load
EPUB Validator Results
Detected version: EPUB 2.0
Results: Congratulations! No problems were found
Yet when I attempt to load in Firefox (Actually Aurora 18.0a2) I get a yellow triangular exclamation point symbol, "Or you can add an exception…" and a 'Try again' button.
Would it be trying to open the contents in secure mode or something?