its more or less what i've already done, in my specific case i noticed that ive properly downloaded files cannot be opened. i tried two mime types: a png file and an apk file (that is basically the updated apk of my current app),..i also noticed that i cannot access folder or files OUTSIDE the storage space of my app. i'm stucked on this point..
files:///data/data/package_name/files/files/file_name.apk
this url cannot be opened by android and i cannot install apk or open whatever file...
i've used file, filetransfer and fileopener2