There's an important bug fix in this release. Exported projects that were uploaded did not work in all browsers (notably Firefox 5). This should be fixed in this release. However, to fix projects that you've already uploaded, you'll need to open in this build, export again, then re-upload.
New this build: bundled WebStorage plugin, and sprites can auto-mirror and auto-flip like in Classic!
However, this lead to a bigger new feature: Construct 2 now runs a local HTTP server to preview your game! The reason why this has been added is a little complicated - allow me to explain.
Previously, Construct 2 just dumped some files to a temporary folder on disk and told the browser to open the preview.html file (which ends up using the "file://" protocol rather than "http://"). This works fine for most purposes. However, browsers have extremely tight security for the file protocol. It seems over the top to me, but we have to work with it. The new auto-mirror/auto-flip feature required a "read pixels from an image file" operation. Browsers block this for pages on the file:// protocol. Apparently it could be a PNG of a bank statement or something. Oh well. Anyway, if the files are served over http://, the browser security measures are relaxed and the pixels can be read from the image. The files are still on disk! They're just sent via a local HTTP server, which keeps the browsers happy. It's a bit mad, but it works. You'll notice "localhost" in the address bar rather than "C:\Users\...". That's pretty much it, nothing else is changed really.
I never thought auto-mirror/auto-flip feature would end up with me writing a HTTP server, but there you go. All in a day's work at Scirra!