Cimorene

Tools > Options > General > to set the home page. where it says 'use current page' in the latest evrsion, it used to say more clearly 'use current pages'.

point in fact, if you open the various tabs you want so you have the 'set' you wish to use as your 'home', pressing this button will set the whole series of tabs as 'home'.

you can also simply write all the urls on one line and paste that line in the text area and press okay, that'll work too-- the urls need to be separated with |

an example:
http://www.livejournal.com/users/anatsuno/friends/|http://www.journalfen.net/users/anatsuno/friends|http://www.boingboing.net/

ALSO. my thingie i should make a ppost out of for all those new firefox users: go and dig around in the extensions http://texturizer.net/firefox/extensions/ - they are little plugins, basically, to download and install on top of firefox. some of them are really neat.
the 3 ones i always install are Deepest Sender (LJ client, useful for not having to log out of semagic for RPG posts purposes, for example, or JF posting, or whatnot), Quicknote (a great blogging help and all purpose note-taking utility omg loff) and Tabbrowser Extensions, which allows you a lot of extra nifty tricks on top of the native tabbed browsing of Firefox.

/geekery omg