Use Clang compiler instead of GCC Build with user-specified compiler optimizations (-Os, -O0, -O1, -O2, -O3) from CFLAGS (unsupported) Disable EME (DRM plugin) cabability at build time Enable WebDriver support Allow Gecko Media Plugins (binary blobs) to be automatically downloaded and kept up-to-date in user profiles Force-enable hardware-accelerated rendering (Mozilla bug 594876) Allow to disable screenshot extension in global profile Use the system-wide media-libs/harfbuzz and media-gfx/graphite2 instead of bundled. Use the system-wide dev-libs/icu instead of bundled. Use the system-wide media-libs/libjpeg-turbo instead of bundled. Use the system-wide dev-libs/libevent instead of bundled. Use the system-wide media-libs/libvpx instead of bundled. Use the system-wide dev-db/sqlite installation with secure-delete enabled