As Firefox 57 is on trunk, we are shipping e10s by default. This means that
our primary support is for e10s. As part of this, there is little to no need
to run duplicated tests in non-e10s and e10s mode.
In bug 1386689, we have turned them off. There was some surprise in doing this
and some valid concerns expressed in comments in the bug. Given that, I
thought we should bring this information to a wider audience on dev.platform so
more developers are aware of the change.
While we get some advantages to not running duplicated tests (faster try
results, less backlogs, fewer intermittent failures) there might be compelling
reasons to run some tests in e10s based on specific coverage. With that said,
I would like to say that any tests we turn on as non-e10s must have a clearly
marked end date- as in this is only a temporary measure while we schedule work
in to gain this coverage fully with e10s tests.
Also keep in mind that most if not all of the CI/scheduling/admin benefits of
turning off the tests are already accounted for with the new stylo tests we are
running in parallel on osx and windows.
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