A question was asked in #linux how to load up a group of URLs in tabs from the console. The documentation was less than awe-enspiring, but at least gave the clue that opening a single URL is done as mozilla "url".

Then, I remembered that when a group of URLs is saved as a home group, the input box that shows the current setting separates all URLs by pipe symbols. So, to load a group of URLs from the console, try this: firefox "URL1|URL2|URL3".