To amplify somebody else's advice: Perhaps you should add the directory containing `xulrunner-gtkmozembed.pc' means that xulrunner-gtkmozembed.pc isn't there. To find it, go to http://packages.debian.org, find the form at the bottom, fill in xulrunner-gtkmozembed.pc in keyword, pick the correct distribution, and hit search. Bingo, you know what package xulrunner-gtkmozembed.pc is in. Repeat the next time you seem to be missing a purticular file.

To give new advice: Use <c> tags, not <pre> tags, on PM; they'll wrap long lines according to the user's preference, thus keeping the page from becomming horribly wide and difficult to read.