Yes. Set the home page so both links are entered with a | is between the links. Example: Google.com|Yahoo.com

https://support.mozilla.org/en-US/kb/how-to-set-the-home-page

Using the pipe (|) symbol only works for tabs in the same window. For multiple windows you likely need to use a script file to be able to specify startup parameters with -new-tab and -new-window switched and URLs between them.

On Linux this would be this code and I assume that on Mac this will work as well. Make sure to set the executable flag on the file. You can find the Firefox installation path on the "Help -> More Troubleshooting Information" (about:support) page.

#!/bin/sh

cd <path to firefox>
./firefox --new-tab URL1 URL2 --new-window URL3 URL4

Well, this is getting beyond my pay grade! But I appreciate the help!

I don't use a home page but I want the same windows and tabs when I restart the browser. I leave the windows and tabs open when I exit the browser and have the setting "Open Previous Windows and Tabs". That is the first setting, at the top of the General page in Settings.