www-client/firefox: add a missing dep to 96.0

Signed-off-by: Joonas Niilola <juippis@gentoo.org>

www-client/firefox/firefox-96.0.ebuild

@@ -136,13 +136,14 @@ CDEPEND="
 	>=dev-libs/libffi-3.0.10:=
 	media-video/ffmpeg
 	x11-libs/libX11
-	x11-libs/libxcb
 	x11-libs/libXcomposite
 	x11-libs/libXdamage
 	x11-libs/libXext
 	x11-libs/libXfixes
 	x11-libs/libXrandr
 	x11-libs/libXrender
+	x11-libs/libXtst
+	x11-libs/libxcb
 	dbus? (
 		sys-apps/dbus
 		dev-libs/dbus-glib