I noticed there are some incompatibilities between FileAPI and mimesniff tests.

If we make Blob spec compliant, mimesniff tests will fail and viceversa

If the type member of the options argument is not the empty string, run the following sub-steps:

1. Let t be the type dictionary member. If t contains any characters outside the range U+0020 to U+007E, then set t to the empty string and return from these substeps.

2. Convert every character in t to ASCII lowercase.

e.g. #2 conflicts with the following test in mimesniff

From MIME Sniffing spec:

4.4. Parsing a MIME type
To parse a MIME type, given a string input, run these steps:

1. Remove any leading and trailing HTTP whitespace from input.

#1 conflicts with the following FileAPI test: