Allow user to provide location when starting Firefox.

[Garbee]

Associated Issue: No direct issue. Precursor to simplifying the getting started flow brought up in issue #1127.

Summary of Changes

Firefox startup bin now takes an optional location parameter. If not provided, it defaults to about:blank as that is safe for a fast startup for a developer to use it. We also know that exists always, so it won't cause the terminal to dump out needlessly.

Testing

• passes npm test
• passes npm run lint

[jasonLaster]

👍

nice use of url.parse, url.format.

This solves the problem where a user does:

npm run firefox
npm start

and is surprised that firefox opens to an error page and is not connected with the debugger.

The reason it failed was that previously it was trying to go to todomvc, which was an examples' server route and the server had not yet started.