Buildbot/Talos/Internals
From MozillaWiki
Order of Operations
For each test a new profile is installed in the browser (either an empty base profile or a profile with an existing places.sqlite in case of the dirty tests). Profiles are not shared across test runs. To initialize the profile an initial open/close is done to the browser. This initial open/close is not included in the test results and is only for configuration purposes.