MediaCoder has some part of its GUI written with XUL which requires Mozilla's Gecko engine to render. The easiest way to get Gecko is by getting Firefox, which is actually an application built on Gecko engine with XUL. However, as is reported by some users, MediaCoder's XUL interface is not working as expected in their Firefox. Also some people don't want to accept Firefox to be installed into their system for some reasons. An alternative to get XUL interface shown is by using XULRunner, the XUL runtime package. It is exteremely simple to get MediaCoder work with XULRunner. First, download XULRunner and extract the files from the package to some place. Start MediaCoder and go to Options menu and choose Browser setup. Click the "..." button, navgiate to the XULRunner folder and choose xulrunner.exe. Click OK button to confirm and it's done.