My default web browsers at the moment are all Gecko based. On my new WinXP Pro machine at work I'm using Phoenix 0.5 (very cool), at home on my Win2k box Mozilla 1.2.1 and Phoenix 0.5 are currently fighting it out to see who' ends up the dominant browser (at the moment my money's on Moz, as I do use it to pick up my POP mail on that machine). The XP Home laptop is still running Phoenix 0.4, mainly because that's got everything I need on it at the moment and I haven't got round to upgrading it yet.
To be honest Mozilla is my favourite internet application suite, it does have nearly everything I ever need for surfing the web, checking my email and testing my web applications. Phoenix is smaller, faster and prettier and so is great for general web browsing but is still missing a few features for the more advanced web stuff, it's great that they've got the Javascript console back in again, but currently my big Phoenix wants are the "Links Toolbar" (see below for more on this) and the "Style sheet switcher" from Mozilla, but then I guess I'm not your average user so I'm not going to moan.
Great stuff that has recently been added both to Phoenix and Mozilla includes the new Type Ahead Find it is such a time saver on large pages (although it's default mode only searches links, whereas I mainly use it to search through all text on the page, and I'm looking forward to daring to try out the new "Bayesian" intelligent, learning spam filters on my mail accounts (although I do still feel worried about trusting my main email accounts to what is currently pre-alpha level code, although I may give Moz 1.3alpha a quick spin when it comes out just to try this).
Standard add-ons that I install without fail are: for Phoenix Alternate Stylesheet Switcher (to emulate Mozilla's CSS stylesheet switching options) and Text Links both available from David Tenser's Phoenix Help site. For Mozilla the only extension that I regularly install is Tobias L�fgren's minirot13 from http://www.pinkroom.biz/owl/minirot13/