By default SharePoint 2013 web applications have the browser file handling level set to strict. This setting works with the browser to prevent files from being opened automatically by the browser for enhanced security. Setting this property to permissive would invite unneeded security risks so leaving it at strict is in everyone’s best interests. However there may be some files in your organization that you want to enable SharePoint to open automatically when browsed. HTML files are one example file type that you may want to have open directly in the browser rather downloading and then opening.
Luckily we can specify specific file (MIME) types to be exceptions to the strict rule. By using the following powershell excerpt we can see what file types are currently excluded from the strict setting:
$webApplication = Get-SPWebApplication "http://yourwebapplicationurl" $webApplication.AllowedInlineDownloadedMimeTypes
To add a new file type we just need to add the corresponding MIME type to the list:
$webApplication = Get-SPWebApplication "http:/yourwebapplicationurl" $webApplication.AllowedInlineDownloadedMimeTypes.Add("text/html") $webApplication.Update()
Verify that it has been added by viewing the AllowedInlineDownloadedMimeTypes again and you will see it has been successfully added and these files types should now open directly in the browser.