SimpleTest.requestFlakyTimeout

Interesting: http://mxr.mozilla.org/mozilla-central/source/testing/mochitest/tests/SimpleTest/SimpleTest.js#656

/**
 * Request the framework to allow usage of setTimeout(func, timeout)
 * where |timeout > 0|.  This is required to note that the author of
 * the test is aware of the inherent flakiness in the test caused by
 * that, and asserts that there is no way around using the magic timeout
 * value number for some reason.
 *
 * The reason parameter should be a string representation of the
 * reason why using such flaky timeouts.
 *
 * Use of this function is STRONGLY discouraged.  Think twice before
 * using it.  Such magic timeout values could result in intermittent
 * failures in your test, and are almost never necessary!
 */

That means that the current usage of SimpleTest.requestFlakyTimeout should be removed as much as possible. That sound like an interesting little project to work on, there are currently 586 instances of this function in mxr: http://mxr.mozilla.org/mozilla-central/search?string=SimpleTest.requestFlakyTimeout

Mochitests that rely on bfcache

A lot of the intermittent failures ("oranges") that are happening on the test machines, are race conditions, like low memory conditions/high disk usage/slow web server/etc.

When trying to fix one of those intermittent failures, I noticed how that test is able to fail: it is relying on bfcache to work.
Especially on mobile, that is a bad assumption.

One thing that could be improved is to clear the cache after each mochitest. But I also think the tests themselves shouldn't rely on bfache to work (unless of course, they are testing bfcache). So I filed bug 1057499 and pushed a tryserver run there to see how things go with bfcache turned off. Could be interesting.