1. Firefox's "awesome bar" - When you start typing in Firefox 3's address field, the browser searches a database combining both your surfing history and bookmarks. Knowing what sites you visit most often, it presents a list of choices almost instantly, and is frighteningly good at figuring out what you want. For me, the awesome bar is so accurate that it's made bookmarks obsolete.
3. Internet Explorer 8's tabs - My favorite feature in IE8 makes good use of what was once wasted space:The default page that appears when a new, blank tab is generated. It lets you open previously closed tabs, shows you what's hiding in your clipboard and gives you access to IE8's new Accelerators feature. IE8's tab management is also very good, clustering and color-coding related tabs.
4. Firefox's bookmark manager - This is the engine on which the awesome bar is based, and nothing beats it for fast searching of bookmarks and history. Its layout is also simple and intuitive.
5. Safari 4's full-page search - When you do a search in Safari's history, it parses not just the page titles and Web addresses, but also the text found on the pages when you last browsed them. This makes it much easier to find sites, because you don't have to remember a URL or a page name, just a snippet of the text on the page itself.
6. Chrome's updates - As with most Google products, minor updates to Chrome are delivered silently. You don't even know they're been added. This may be irritating to some folks who want complete control over what's uploaded to their systems, but I would prefer not to be bothered with .0.0.0.1 updates.
7. Firefox's extendability - The number of add-ons and extensions for Firefox are legendary. While I'm not a big user of them, I appreciate that they're there when I need them. If you need a specific feature in Firefox, chances are there's an extension that will do it.
8. Safari's User Agent - Safari's developer tools let you tell a Web site that your browser is something other than Safari. Safari 4 can spoof anything from the iPhone's browser to Internet Explorer 8.
9. IE8's security features - OK, stop snickering. Yes, IE has a history of being a sieve when it comes to security, but IE7 made great strides in locking things down, and IE8 is even better. With improved anti-phishing protection, its new InPrivate browsing (which is NOT anonymous browsing, but rather wipes all traces of activity from the local machine), interaction with Windows Vista and Windows 7 parental controls, and domain-name highlighting, IE8 contains more features to help keep you safe.
10. Chrome's most-visited - While Safari 4 made headlines this week with its slick Top Sites feature, Chrome did it first and with a cleaner, simpler interface. This feature shows thumbnails of your most-often-visited sites in a grid. It loads quickly and gets more useful over time.
This list is purely subjective, of course. Any browser that incorporated all these features would get my love.
What features would you like to see in the perfect browser?