Use an explicit 'subtest' query parameter to select the subtest, instead of just a naked number. Mozilla sometimes appends query parameters to its tests for its own reasons and those parameters should not accidentally trigger selection of a subtest. Also, don't use one or two iframes per subtest; it saves a lot of memory and time to use one or two iframes per test and have the subtests reuse those frames.
Merge pull request #397 from rocallahan/submission/rocallahan

Use an explicit 'subtest' query parameter to select the subtest, instead...