I cannot tell why this happens, but it probably is some malconfigured security setting inside Firefox. Maybe in combination with a malconfigured upload (or download requrest!) that Chrome will catch, but FF does not.
Try this when ff shows the blocked page warning.
Show source.
Save page as and name it as a zip.
If the page really were blocked, ff would not have downloaded it all. So it is less a blocking, and more of a ff not realizing, it should download the thing, instead of displaying it.
