In Firefox: - on the top menu under bookmarks there's a choice to "bookmark all tabs". If you open tabs to, for instance, all your representatives (and close all others), then choose that, you'll have them there. You name the bookmark "folder" to indicate them, and then when you want to send a message you simply choose it; one of the choices in that bookmark is to "Open all in tabs" A similar choice is in Safari.
I don't think you can do this in IE yet (Starling?) although it will be in the next release.
It's also possible in firefox to set all your favorite bookmarks as your start page. Since I use gmail, and my own igoogle page for all my pet things, I have my start page set to open those tabs - and Calendar - at the same time when I start up in the morning. (I don't turn off the computeer but i do close the browser.)
I'm using Firefox too, and I don't think IE has a way to keep the tabs that way. You can also choose to open multiple tabs instead of one home page when you open Firefox. I'm not doing that, but I could see how it would be useful.
I also love the fact that if I type a single letter in the address box it gives me a selection of URLs, with the one I use most with that letter at the top. I hit "s" for this site, for example, and "d" for another forum I go to a lot. Very useful especially because I don't need to begin to type Alzheimer's to get to this site. Just an "s" for Spouse. That "s" also gets me to the blog about Sephardic foods. It is a couple of options down from this site since I don't go there as often.
It only offers you sites that YOU go to, so for it to work you have to have gone there at least once or twice before it will show up in the options.
You can open multiple tabs for different home pages on IE but I don't think you can use them to send out mass mailings. If you can, I don't know how :)
No, you wouldn't use them to send out mass mailings: you just make a bookmark folder with the urls for all of your reps, open it, opening all the pages at once, then quickly page through each one individually and paste in your message in their 'contact me' page. Saves having to hunt them up one by one.