The new version of Twitbin (2.0) is much, much better than the previous release and really puts it back into the running as a contender. In fact, the only reason that I started looking for an alternative is because I found Twitbin to be pretty much broken--but that was the old version.
So I love love love the RT (that's "Retweet" for you non-Twitterites ... a RT is when you basically twit out someone else's tweet in order to help spread the word to your follows; it's basically a "pay it forward" form of good-will on Twitter) function in Twitbin; I don't know of any other Twitter extension that offers the ability to RT with the click on an icon.
There's a problem with the @ function, though (@ is when you direct a message to a certain user but keep it in public; it remains on the public timelines but it's sent to their attention--it's basically used to respond to other people's twits). Well, two problems, actually: (a) When you click on the "@" icon to respond to someone, the text entry window does not focus. You have to manually click your mouse into the text entry window. What's more, (b) you have to hit your space bar before you begin typing. While clicking on the "@" icon copies "@
I love how you can ♥ a tweet. When you click on the ♥ icon, you basically add the current tweet to your list of "Favourites" on Twitter, which people can view when they go to your Twitter URL (http://twitter.com/[twitterusername]/).
To me, the "i" icon is a bit redundant; it takes you to the user's Twitter Page, which you can also do by clicking on their icon picture.
I really like that you have the option of displaying tweets from your Friends, your @s, your DMs, your ♥s, and from the public timeline (which includes EVERYONE on Twitter and, quite frankly, is very busy!).
Now, there's one other major deficiency with Twitbin 2.0 that I see: there's no way to respond to DM (that's Direct Message for you non-Twitterphiles--essentially, a private message between two Twitterers that's not on the public timeline) via a DM by simply clicking on an icon, like there is to reply to an @ message (even though it's a bit buggy). In the "D" list, there should be a little "d" icon that, when clicked on from a DM directed toward you, should do the following: (a) place the text: "d [TwitterUserName] " into the text input box and (b) focus the text input box with the cursor after the space, after the username.
That's not all that difficult now, is it? Twitterfox has managed to do it.
Speaking of Twitterfox, while I appreciate their "Recent," "Replies," and "Messages" tab, I don't think it's necessary to spell it all out as they do. To me, Twitterfox would be more useful if it were transparent and then became solid on-hover (when you hold the mouse over it). As it is, it blocks too much of my screen real estate (I'm working via a notebook computer, not much I can do to upgrade the resolution or anything). Twitbin sits in the sidebar which I usually don't have open but now, I'm finding I prefer the sidebar as opposed to coming onto my screen. Neither is ideal but for me, the preference is sidebar.
What I do like about TwitterFox is that it shows you the number of X-type of Twits that you have awaiting you. For instance, I just signed into TwitterFox and and it's telling me that I have 19 Recent, 20 Replies, and 20 Messages since my last login with them. I also really like how there's an icon to "insert current tab's URL" into the text entry box; however, it would be MUCH more useful if TwitterFox shortened the URL in the current tab (via a URL-shortening service such as TinyURL).
Additionally, the text-entry box in TwitterFox grows as soon as you start typing something in there and won't shrink back (even if you clear everything out) until you hit enter. That's not-so-cool.
So Twitbin, are you listening? Make these changes and I think you'll have a killer Twitter add-0n for Firefox! BTW Twitbin, why don't you have a Twitter accoutn linked from your web site so we can follow you???