I'm one of the types of users that our ITS department hates - with a minimum of half a dozen apps open & running all the time and a crowded task bar.
For a long time I used Lotus Notes (standalone workstation) for my browser and email client, and was happy with it until fairly recently. I have also tried Opera browser & email client, and have only one really big objection to it - it is dificult to impossible (for me anyway) to formet text and backgrounds on the fly in emails.
I realize browsing and email client software is quite different, but I would still prefer having one app that did both, maybe with a calendar & other stuff too. However, I most certainly do not have the expertise needed to attempt to combine Firefox & Thunderbird.
Add to that - I have a latent distrust for Mozilla email products based on past experiences with Netscape Mail. I'm using Thunderbird tho, for now at least, and to be fair - I haven't had any problems with it.
At work we're solid MS customers (victims?) with IE and Outlook. I cheat with the browser tho, I use Avant Browser which is an IE browser with tabbed browsing. Pretty cool if, like us, you're stuck with MS products.
Radar