I've uploaded Send Tabs version 0.1, modified from the original for compatibility with Firefox 1.5 - 2.0.
sendtabs-0.1.xpi (3 KB; English (United States); compatible with Firefox 1.5 - 2.0.0.*)
Send Tabs works by enumerating the URLs of all open browser tabs and sending that list, along with a default email subject line, as a "mailto" URL and passing it to the "mailto" protocol handler which invokes the system default email client. It works very well until the maximum of ~462 characters (subject line + URL list combined) is exceeded; at that point you get an error.
That glaring limitation makes Send Tabs useless if you have a lot of URLs to send. The goal of the next few milestone releases is to overcome this barrier.