When we are accessing any HTML pages from SP 2010 site, we will see a popup with download option.
This is default behavior of the SP 2010 sites. We need to change the “Brwoser File Handling” to Permissive.
1. Log in to central admin and select the corresponding web app.
2. From the ribbon, select General settings dropdown.
3. In the general settings page, set the “Browser File handling” to “Permissive”.