I have been using Chrome as default browser for a while apart from using Firefox for web development. One thing I noticed is that Chrome downloads index files instead of displaying the page in some websites. There is a discussion on Chorme help forum shows that the problem is caused by Internet Download Manager (IDM). The solution is to opt-out the Chrome from Advanced browser integration under General tab in IDM Options. Just click Downloads->Options and under General tab, opt-out the Google Chrome. See the snapshot below. I hope this help you too.