If you open too many URLs in Firefox at once you will probably crash it. But anyways.

1. You can do it via a command line. If you were on Windows, Start Menu => Run => type "cmd.exe" => type:

<pre>"C:\Program Files\Mozilla Firefox\firefox.exe" http://google.com http://eyesonff.com http://whatever.com</pre>
They will open in tabs. You can copy/paste the list of URLs onto the command line to avoid typing.

2. If you make a bookmarks folder, and make a bookmark for each URL and put it into that folder, you can middle-click the folder and open all bookmarks at once in tabs. If these URLs are ones you'll have to re-visit many times, this may be a good option.