Firefox, but there's one thing I'd change about it: the history. It's too hard to find a page again which I know I viewed recently, where I know the site it's from but I just can't remember exactly when I last viewed it.
In the history sidebar, viewing the history by site doesn't list all pages in your history properly. It lists all the web pages in your history, in alphabetical order by the page title - not even the visible title shown on the page, but its title as given by the page author in the head section of the page's HTML metadata, i.e. it's a "behind the scenes" title.
Here's what my history "View By Site" looks like in version 2.0.07:
Surprisingly, someone reported this as a bug only relatively recently, in April 2007. I should have got off my butt and reported it myself much earlier, as it's been bugging me ever since I got Fox, but I didn't want to moan publicly too much. So all I did was forlornly do a search once in a while to see if anyone had fixed the problem, then moan quietly to myself and grumble a bit when I still couldn't find anything.
Well, I can now say - Huzzah! I've just noticed that the official Win32 20070823 [Trunk] build fixes this issue. (If you want to download it use the "All.. hourly builds for the last 14 days" link, if the others are broken.) I've now downloaded version 3.0a9pre (Minefield). See this screenshot:
All organised into nice neat folders, grouped by main domain URL of the site. Look at the difference, and drool! (OK, I'm sad like that.) It's so much more usable from a consumer and personal information management point of view.
I'm not going to use Minefield as standard because it's still experimental and I'm a scaredycat, plus more to the point my essential extensions like Greasemonkey don't seem to work with it yet.
But by downloading Minefield, I can now just use it whenever I need to view my Fox history by site in a grouped folder way. (Note: you need to close all existing open versions of Firefox before you try to launch Minefield's Firefox.exe from your unzipped download folder, or it'll just open your existing version of Fox.)
So now you too know how to view your Firefox history by site, organised properly by site into folder groups, pending the release of 3.0, and if you need that feature you could try doing the same.
Huzzah, I say again! I can't wait for 3.0!