Since multiprocess is in the regular Nightly, the code is in the main line of development (mozilla-central). Based on the preference, it decides at runtime how

Since multiprocess is in the regular Nightly, the code is in the main line of development (mozilla-central). Based on the preference, it decides at runtime how to handle the content/chrome interface. But when Mozilla does branch off separate trees, VCS merges and lots of automated tests are largely sufficient.