Consider editing a HTML file and you want to open that file in your webbrowser. Well, that's easy but you want to open the file as a URL. You have edited it in the folder of your webserver application (C:\inetpub\wwwroot... for example) and it should open it as the URL localhost/....
This package does the right thing. All is done in the run_in_browser.py. To customize you can change the following:
Change the replace path: url = url.replace('C:/inetpub/wwwroot', 'http://localhost'). In detail:
Change the path to your webserver (here: C:\inetpub\wwwroot) to the path where your webpages are.
Change the host (here: localhost) that replaces this part in the webbrowser.
Change the call of your favorite webbrowser (here: "C:\Program Files (x86)\Mozilla Firefox\firefox.exe").
Change the shortcut: The package defines a keyboard shortcut CTRL-F11 (like in Eclipse) to open the file in the webbrowser. You can change/remove the shortcut in the Default (Windows).sublime-keymap file in the package itself.
I haven't set any keymaps for Linux or OSX. I even don't know if this works on this OS.