Comment 7 for bug 1718885

I'm not at the kiosks now and can't run apt-cache, but I did run ldd earlier, and can report that for the Chromium binary (/usr/lib/chromium-browser/chromium-browser) ldd reports libffmpeg.so as not found. That's why the shell script /usr/bin/chromium-browser sets LD_LIBRARY_PATH=/usr/lib/chromium-browser before executing the binary. That allows libffmpeg.so to be located for regular users, but not for guest users -- as I noted, I think that's because of the interaction of the AppArmor "Cx" setting for Chromium, which causes the environment variables to be scrubbed just before the binary is executed. That's my guess, anyway.