Make compilation of mozilla plugin easier on different distributions. Removed fixed include paths from mozilla/Makefile.am. XPIDL_INCL is automatically determined from ${MOZILLA_CONFIG}. 
Configure and compile with XPIDL=<path_to_xpidl> application of your mozilla version, eg for mozilla-1.7.6 use: XPIDL=/usr/lib/mozilla-1.7.6/xpidl ./configure <rest of line> && make