Does File > Save Page As not work? You should be able to load the page and then read the source code with a plain text editor.

You may be interested in Firefox's built in tools

• https://developer.mozilla.org/en-US/docs/Tools/Web_Console#The_command_line_interpreter
  (Scroll the page for more features.)

If a page is generated via JavaScript then probably your option to get the generated source would be to save the rendered page in a browser. You can't do that in a terminal window AFAIK via command line arguments, but you can open the page.

To save the "rendered" source, in the past, I've used this approach (Windows keyboard shortcuts):

• Select all using Ctrl+a
• right-click > View Selection Source
• Ctrl+S to save from the source viewer

Another way is to use the Inspector (right-click the page > Inspect Element), scroll to the top of the HTML pane, right-click the html element, and choose Copy Outer HTML. Then you can paste into the editor of your choice.

Actually, I haven't compared the two. Hmm...

Edit: I didn't really understand the "terminal" part when I posted this. Never mind.

Just used phantomjs