GeckoFx-14.0 only looks for /usr/lib/firefox on Linux (https://bitbucket.org/geckofx/geckofx-14.0/src/2f17d126989221001ce8d7f8a6b0b7949216fbac/Geckofx-Core/XULRunnerLocator.cs?at=default), so I don't think XULRunnerLocator in it's current form would work for us.