Before using try, there is some recommended configuration you should set up. This can be accomplished by running:
$ ./mach mercurialvcs-setup
Be sure to at least enable the [http://mozilla-version-control-tools.readthedocs.org/en/latest/hgmozilla/firefoxtree.html firefoxtree extension] and the push-to-try extension. The push-to-try extension is required if you wish to use the |mach try| command (see below). Firefoxtree will give you a handy 'try' alias you can use for pushing, and prevent you from accidentally pushing multiple heads. If for some reason you prefer not to use firefoxtree, you can set the same alias up manually in your hgrc: