Firefox was started with the intention of taking the best of the Mozilla browser suite and stripping it back to create a small, fast browser equally at home on any of the main operating systems.
Firefox features all of the usual browser innovations including pop-up blocking, tabbed browsing and integrated search, and thanks to its growing popularity, it is supported by most banking sites. There are still occasional sites that will throw Firefoxers into an unsupported browser page, but it's possible to easily change the User Agent String to fool a site into thinking it's seeing Internet Explorer on Windows XP. Fortunately, this is a very rare occurrence.
The popularity of this browser also means that the likes of Google, Yahoo! and Amazon have all released Firefox-specific versions of their toolbars which can be used to access a range of services from these providers. Installation of extensions is easy, thanks to the XPI system, and as development of the application is a public affair, there are tons of extensions available, from Gmail readers to FTP clients.
RSS technology is integrated into the browser in a very smart way: when you navigate to a site with an RSS feed available, an icon appears at the bottom-right of the main window. Clicking it will add the feed to the bookmarks menu (or toolbar), and this bookmark becomes dynamic - constantly updating to reflect the changes in the site. Select a story from the bookmark to jump to the page.
Firefox is an excellent Safari replacement. It's free and benefits from an increasingly high profile. While it may not feel familiar to long-term Mac users, it does a good job of staying consistent with the OS, but you may miss services Speech which the more 'native' browsers support.