TV* jobs run against test files that have been modified; this is an attempt to find intermittent failures introduced by recent test changes. Note that TV* runs as tier 2 -- you shouldn't ever be backed out for failures in TV. More info at https://developer.mozilla.org/en-US/docs/Mozilla/QA/Test_Verification.
The failures are:
TVg1: Per-test run of ...\overflow-hidden-details.html: : FAILURE
TVg3: Per-test run of ...\overflow-auto-details.html: : FAILURE
What is happening here is that TV thinks these are tests, but they are not. TV thinks they are tests because they appear in reftest manifests; they are not test files though, but reference files. Run 'mach reftest layout/reftests/details-summary/overflow-hidden-details.html' and you'll see that no tests are run. TV is doing the same thing and getting the same result. In automation, 0 passes translates into a failure. This is basically a dup of bug 1406407, which I hope to make progress on this year.
In summary, sorry for the confusion, and there's probably nothing for you to worry about here.