IntelliJ does a foolish thing when you "Make" a Gradle-based project: it asks Gradle to build app:assembleDebug, library1:assembleDebug, ..., libraryN:assembleDebug. Due to an implementation quirk, the Debug variant of :app relies on the /Release/ variant of :library1 through :libraryN. So we end up building both Debug and Release variants of each library. (I think.) See http://tools.android.com/tech-docs/new-build-system/user-guide#TOC-Library-Publication. We should experiment with hard-depending on specific configurations in our build.gradle files. I expect we can trim our build time in IntelliJ. (From the command line, I always use just |mach gradle app:{assemble,install}Debug|, which should not do duplicate work.) Code snippets are available at https://code.google.com/p/android/issues/detail?id=52962 and https://code.google.com/p/android/issues/detail?id=66805. For information radiation: Android Studio has a more clever thing, which they call "Gradle Aware Make".

Re-triaging per https://bugzilla.mozilla.org/show_bug.cgi?id=1473195 Needinfo :susheel if you think this bug should be re-triaged.