linux 2.6.39, GCC 4.6.0 Compiled and installed XULRunner 5.0.1. I don't know how to test it, so I assume it's ok. Compiled firefox 5.0.1 with use_LIBXUL_DIST.patch and the correct configure switches --with-system-xul --with-xul-sdk=.... or somesuch. Running firefox ALWAYS gives this response: Could not find mozilla runtime. I tried replacing /usr/bin/firefox with a symlink to /usr/lib64/firefox-5.0.1/firefox. I tried renaming it firefox-bin. I tried editing run-mozilla.sh to call 'firefox' instead of 'mozilla-bin'. I tried export PATH=$PATH:/usr/lib64/xulrunner-5.0.1:/usr/lib64/xulrunner-devel-5.0.1/bin:/usr/lib64/firefox-5.0.1 export LD_LIBRARY_PATH=/usr/xulrunner-devel-5.0.1/lib:/usr/lib64/firefox-5.0.1 I tried recompiling. I searched the source tree and the build tree for 'firefox-bin' and 'mozilla-bin'. Not found. I tried compiling firefox 3.xxxx, but it will not compile with GCC 4.6.0. It wants -fpermissive, but adding that to the mozconfig file made no difference. Trying 'alias c++="c++ -fpermissive"' made no difference. Trying CXX="c++ -fpermissive" made no difference.