We're releasing a hotfix that will fix these, which you'll be able to get to via some KB articles. These KBs with fixes are live and are the best way to update your system. The fixes solve the browser-detection issue forever for all sites on a machine. These will be rolled up into future versions of the framework and will eventually also be on Windows Update.
.NET 4 - http://support.microsoft.com/kb/2600088
.NET 2.0
http://support.microsoft.com/kb/2600100 for Win7 SP1/Windows Server 2008 R2 SP1, Windows Vista/Server 2008, Windows XP/Server 2003
http://support.microsoft.com/kb/2608565 for Win7/Windows Server 2008 R2 RTM
What the fixes do is update the ie.browser and firefox.browser files in \Windows\Microsoft.NET\Framework\<version>\Config\Browsers with new and future-proofed versions of these browser definitions. Nothing else is affected.
App_BrowsersIf you don't have access to the whole machine and/or just want to update a single project, use NuGet to install the App_BrowsersUpdate package. Your site structure in Solution Explorer will then look like the image at right. Note that NuGet uses .NET 4, so for systems that have only .NET 2, you'll need to get the ZIP file and put the new browser files in App_Browsers manually.
.NET 4 Browser Update NuGet Package - http://nuget.org/List/Packages/App_BrowsersUpdate
install-package App_BrowsersUpdate
.NET 2.0 Browser Update NuGet Package - http://nuget.org/List/Packages/App_BrowsersUpdate.net20
install-package App_BrowsersUpdate.net20
Note that NuGet is VS2010 specific so if you don't have nuget.exe and .NET 4, you can also copy the .NET 2 updated browser files into ~\App_Browsers manually from this zip file.
Updating the whole machine is the preferred way to fix this.
Статья   http://www.hanselman.com/blog/BugAndFixASPNETFailsToDetectIE10CausingDoPost