We have a 330 second timeout by default: https://dxr.mozilla.org/mozilla-central/source/testing/mochitest/runtests.py#2269 This is a timeout on output from the browser, so if there are test cases which show up here, they need to be modified to ensure we output something to keep the browser alive. The goal would be to reduce this to 30 seconds and modify all tests as needed.
Since tests run at different speeds on different platforms, we may find that platforms like Android and B2G require longer timeouts than most desktop platforms. If so, a technique like this could be used: http://hg.mozilla.org/mozilla-central/annotate/d56c816b35c3/layout/tools/reftest/remotereftest.py#l397 based on 'os' or something like that instead of 'debug'.
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