Use one of these:

• Firefox > Web Developer > Page Source
• Tools > Web Developer > Page Source (Ctrl+U)
• Right-click on a web page to open the right-click context menu and select Page Source

Thank you cor-el, not sure how to accomplish the first bullet, but both of the last two work,

The first bullet applies if the menu bar is hidden (View > Toolbars) and you see the orange Firefox menu button instead.

Click anywhere on the Web page, except on a link or image, for a menu to appear. Windows users will need to right-click to generate this menu. Mac users can simply hold down the 'Cmd' button and then click your mouse or track pad. When the menu appears, click 'View Page Source' and a new window will open with all the source code for that particular page.

Better late than never on my response. But this is just so much easier than all that other stuff.