This can be done with home pages. Firefox can store multiple home pages, for details of how to set all of the tabs as home pages see the How to set the home page article. Once you have them set, in the same part of the Options dialog that you set the home page, change the setting "When Firefox starts" to "Show my home page" .

Another method is to create a folder in your bookmarks and bookmark all of those sites into that folder. You can then use the "Open All in Tabs" option in that folder to open all of the sites.

If it is only for starting Firefox then you can add the (five) URLs to the command line separated by spaces. If you would exceed the maximum number of characters then you need to use a cmd file with the start command to launch Firefox.

See https://developer.mozilla.org/en/Command_Line_Options

You can (or should) have separate Firefox profile folders for each user and create a desktop shortcut to for each user to start Firefox with that profile.

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox