A couple of days ago, to great fanfare, Firefox 1.0 was released. I've been using Firefox as my main browser for months now, and have had no problems, even with the early preview releases. It is a stable platform and standards compliant. It has a built in popup blocker, and plenty of plugins which allow you to change the look and feel, as well as do tasks like monitor gmail and post to a weblog.
It has inbuilt support for RSS (like the one supplied by this site), though I prefer it's sister product, Thunderbird, for this. Essentially, one subscribed to the RSS feed, and when a site is updated the 'live' bookmarks change on the fly.
It doesn't have some of the bugs of Internet Explorer, such as suspect CSS support and incorrect handling of PNG graphic files, and bugs/problems are published and fixed promptly. It's configurable (so if you see no images, be sure to switch them on again. One thing with swapping platform is that you may be prompted to download plugins when you hit flash-ridden pages for the first time - however, this is a case of clicking the 'download the plugin' option.
It is a stable browser, and has been for some time even before this stable release. It remembers your passwords for you (with an optional master password to protect them - I recommend you use it). To top it all, I've not seen a popup in months.
It's multi-platform (WinXP/OSX/Linux)
It has tabbed browsing.
It is also free.
The only problem I've ever had is one website which had a moronic 'which browser are you?' detection script.... never fear, there is a plugin to hop over to MSIE for just this eventuality.