--- a/configure.in
+++ b/configure.in
@@ -1037,17 +1037,17 @@ DIRENT_INO=d_ino
 MOZ_USER_DIR=".mozilla"
 
 MOZ_FIX_LINK_PATHS='-Wl,-rpath-link,$(LIBXUL_DIST)/bin -Wl,-rpath-link,$(prefix)/lib'
 
 MOZ_FS_LAYOUT=unix
 
 USE_DEPENDENT_LIBS=1
 
-_PLATFORM_DEFAULT_TOOLKIT=cairo-gtk2
+_PLATFORM_DEFAULT_TOOLKIT=cairo-gtk3
 
 if test -n "$CROSS_COMPILE"; then
     OS_TARGET="${target_os}"
     OS_ARCH=`echo $target_os | sed -e 's|/|_|g'`
     OS_RELEASE=
     case "${target_os}" in
         linux*)       OS_ARCH=Linux OS_TARGET=Linux ;;
         kfreebsd*-gnu) OS_ARCH=GNU_kFreeBSD OS_TARGET=GNU/kFreeBSD ;;

--- a/python/mozboot/mozboot/archlinux.py
+++ b/python/mozboot/mozboot/archlinux.py
@@ -25,16 +25,17 @@ class ArchlinuxBootstrapper(BaseBootstra
         'zip',
     ]
 
     BROWSER_PACKAGES = [
         'alsa-lib',
         'dbus-glib',
         'desktop-file-utils',
         'gtk2',
+        'gtk3',
         'hicolor-icon-theme',
         'hunspell',
         'icu',
         'libevent',
         'libvpx',
         'libxt',
         'mime-types',
         'mozilla-common',

--- a/python/mozboot/mozboot/centos.py
+++ b/python/mozboot/mozboot/centos.py
@@ -34,16 +34,17 @@ class CentOSBootstrapper(BaseBootstrappe
         self.browser_packages = [
             'alsa-lib-devel',
             'dbus-glib-devel',
             'GConf2-devel',
             'glibc-static',
             'gstreamer-devel',
             'gstreamer-plugins-base-devel',
             'gtk2-devel',
+            'gtk3-devel',
             'libstdc++-static',
             'libXt-devel',
             'mesa-libGL-devel',
             'pulseaudio-libs-devel',
             'wireless-tools-devel',
             'yasm',
         ]
 

--- a/python/mozboot/mozboot/debian.py
+++ b/python/mozboot/mozboot/debian.py
@@ -32,16 +32,17 @@ class DebianBootstrapper(BaseBootstrappe
         'libasound2-dev',
         'libcurl4-openssl-dev',
         'libdbus-1-dev',
         'libdbus-glib-1-dev',
         'libgconf2-dev',
         'libgstreamer0.10-dev',
         'libgstreamer-plugins-base0.10-dev',
         'libgtk2.0-dev',
+        'libgtk-3-dev',
         'libiw-dev',
         'libnotify-dev',
         'libpulse-dev',
         'libxt-dev',
         'mesa-common-dev',
         'python-dbus',
         'yasm',
         'xvfb',

--- a/python/mozboot/mozboot/fedora.py
+++ b/python/mozboot/mozboot/fedora.py
@@ -28,16 +28,18 @@ class FedoraBootstrapper(BaseBootstrappe
 
         self.browser_packages = [
             'alsa-lib-devel',
             'gcc-c++',
             'GConf2-devel',
             'glibc-static',
             'gstreamer-devel',
             'gstreamer-plugins-base-devel',
+            'gtk2-devel',  # it's optional in Fedora 20's GNOME Software
+                           # Development group.
             'libstdc++-static',
             'libXt-devel',
             'mesa-libGL-devel',
             'pulseaudio-libs-devel',
             'wireless-tools-devel',
             'yasm',
         ]
 

--- a/python/mozboot/mozboot/freebsd.py
+++ b/python/mozboot/mozboot/freebsd.py
@@ -18,16 +18,17 @@ class FreeBSDBootstrapper(BaseBootstrapp
             'pkgconf',
             'zip',
         ]
 
         self.browser_packages = [
             'dbus-glib',
             'gstreamer-plugins',
             'gtk2',
+            'gtk3',
             'libGL',
             'pulseaudio',
             'v4l_compat',
             'yasm',
         ]
 
         if self.flavor == 'dragonfly':
             self.packages.append('unzip')

--- a/python/mozboot/mozboot/gentoo.py
+++ b/python/mozboot/mozboot/gentoo.py
@@ -12,14 +12,15 @@ class GentooBootstrapper(BaseBootstrappe
         self.version = version
         self.dist_id = dist_id
 
     def install_system_packages(self):
         self.run_as_root(['emerge', '--quiet', 'git', 'mercurial'])
 
     def install_browser_packages(self):
         self.run_as_root(['emerge', '--onlydeps', '--quiet', 'firefox'])
+        self.run_as_root(['emerge', '--quiet', 'gtk+'])
 
     def _update_package_manager(self):
         self.run_as_root(['emerge', '--sync'])
 
     def upgrade_mercurial(self, current):
         self.run_as_root(['emerge', '--update', 'mercurial'])

--- a/python/mozboot/mozboot/openbsd.py
+++ b/python/mozboot/mozboot/openbsd.py
@@ -18,16 +18,17 @@ class OpenBSDBootstrapper(BaseBootstrapp
             'unzip',
             'zip',
         ]
 
         self.browser_packages = [
             'llvm',
             'yasm',
             'gtk+2',
+            'gtk+3',
             'dbus-glib',
             'gstreamer-plugins-base',
             'pulseaudio',
         ]
 
     def install_system_packages(self):
         # we use -z because there's no other way to say "any autoconf-2.13"
         self.run_as_root(['pkg_add', '-z'] + self.packages)