When it comes to web browsers, Windows 10 gets a little complicated. Internet Explorer 11 is the default browser for now, but later Spartan takes over as it has the new Edge rendering engine (but it can fall back to IE11 for legacy sites).
The Preview 9926 build has Internet Explorer 11 for the browser, however it does have some bits of the new Spartan one coming later this year. Specifically, you can enable the new rendering engine in IE11, the same one that is found in Spartan.
Enable Experimental Web Platform Features
- Open IE11
- Type about:flags in the address bar
- Set 'Experimental Web Platform Features' to enabled
- Restart browser
According to AnandTech, who outlined how to enable this feature, a small number of testers already have this enabled by default. For the rest of you, you can force it to work all the time. However, keep in mind this is literally why it says experimental. As such, you are getting the new rendering engine (that can be fast) but you may also experience some other performance issues.
If you want to live on the edge, try enabling this feature to see the performance difference. Worse comes to worse you can set it back to Automatic or even Disabled, in which case you just use the old IE11 rendering engine.
Additionally, you can also enable the 'Set Custom User-Agent String' function, which may also help circumvent old IE-only content.