The moment they start to integrate somekind of ads (yes, I heard the rumor/plans) in Firefox they are dead. It doesn't even matter if they don't track, aren't intrusive or whatever. The users will run away.
I respect the JSC team a lot but Safari is an active hindrance to anyone trying to ship HTML5 games. It's just a poor-quality browser.
It sounds like you are coming from a web development direction, and are frustrated that Safari doesn't support the web APIs that you care about. As a software engineer, I can sympathize with that.
But as a user, I prefer Safari, because I find that it prioritizes user experience over fidelity to the web page. Examples:
1. Safari was one of the first browsers to ship with a popup blocker
2. Safari defaults to blocking third party cookies
3. Safari Reader cuts out distracting ads and other crap, improving nearly every article. I click it whenever I can.
4. Safari Power Saver defeats annoying animations while saving battery life
I love that Apple is able to deliver features like these, because their fortunes are not tied to advertising.
I also strongly dispute that Safari is slower. For example, I visited cnn.com with Safari and Chrome, and attempted to scroll while the page loads. Safari scrolls responsively, while Chrome and Firefox stutter until the page finishes loading. Things like scrolling performance have a much bigger impact on how my browser feels than any JavaScript benchmark.
It's true that some websites don't work well in Safari, especially HTML5 games. For pages where I want to see that stuff in action, I'll switch to Chrome. But frankly, most web pages are made more usable by disabling newer features. Chrome then becomes a poor man's opt-in.
I use Safari as my main browser for the reasons you mention, but it is slower. It just feels like a cumbersome dinosaur compared to FF or Chrome. And the navigating back flow is less than desirable. I find myself navigating too often to a blank page, or it just seems like Safari doesn't know what to do.
Basically, it does everything great except for the actual browsing part.
If memory serves, recent builds of Firefox (on the non-release channels) are actually starting to roll out OMTC (off main thread compositing) which delivers the same sort of 'performance' you like about Safari, while keeping the perks of Firefox having a faster parser, faster JS runtime, and modern feature set.
You are generally correct that latency is important, though. I don't know if the Chrome dev team prioritizes it much, but Mozilla recently started putting more effort into measuring and reducing latency in various parts of the browser (inattention had let latencies get pretty bad in some places.)
Safari's fortunes aren't tied to advertising because Apple already extracted a payment for every user that runs Safari. They're free to do those things like disable cookies and bundle an ad blocker because they don't have to consider the desires of content creators or generate a revenue stream via their browser. It's the same set of tactics Microsoft was free to use with IE. It's impossible for Firefox or Chrome to offer similar features without directly undermining their revenue sources.
Opera was shipping an enabled-by-default popup blocker before Safari's first public beta, and I'm not even sure if it was first.
Modern IE is a lot better than old IE, certainly; it runs some small subset of HTML5 applications, the javascript performance is adequate, and they have a faster release cycle. However, it still updates less often than Firefox/Chrome, has a worse security track record, and introduces new features on a longer delay. Moving to IE wouldn't make Firefox users any safer or better-served.
http://www.zdnet.com/mozilla-to-deliver-ads-in-its-firefox-b...
It was announced, but no patches implementing anything like this have landed in any code repositories, let alone been released.