Started using Visual Studio 2015 on Windows 10 this weekend, did a clean install. Started bringing in some of our current projects and could not get them to run with a local cert (ssl) on the new IIS Express 10.0. Only seemed to be an issue with Firefox and Chrome, not Microsoft Edge.
To test I setup a Default MVC Project and set IIS Express (via F4 on the Project) with "SSL Enabled" to true, this gave me the url https://localhost:44300 for my project, you may get a different url on your machine.
On Firefox (version 39), asks the trusted cert question, told to trust, nothing happen, go to the http only it works fine.
On Chrome (version 44.0.2403.125), we get ERR_SPDY_INADEQUATE_TRANSPORT_SECURITY error.
On Edge, the site comes in fine.
I primarily use Firefox for development, so my focus was on getting that to run first. Turns out there is something wrong with the HTTP/2 (SPDY) protocols, either with IISExpress/Firefox/Chrome. As a band aid to get this to run, you can go to about:config in Firefox, search "http2" and set them both to false
After this, my local site running on IIS Express 10.0 works just as you would expect. I haven't looked for a way to do this in Chrome yet, but will update this post when I do. These kinds of things are expected in bleeding edge, but I'm very surprised Visual Studio testers didn't catch it.
Update 10/8/2015 Chrome
"Thank you for reporting this issue. As you pointed out in #1, TLS_RSA_WITH_AES_128_CBC_SHA is blacklisted by the HTTP/2 specification. Chrome complies with the specification when treating this as a connection error. Therefore this is working as intended." -- quoted from https://code.google.com/p/chromium/issues/detail?id=529994
Based on this information, it appears that a cipher reorder is the solution, here is a reported working order, haven't tried yet myself.