I'm using office 365. I would like to be able to click on an html file in the document library and have it open in the browser instead of prompting me to download. How would I do this?
I'm quite sure this answer from support is still valid, even though it was written pre SP 2013:
"I understand that you'd like to open HTML file in browser directly but not download it. The issue that you are seeing is by design. This is because of the way that permissive file handling works with SharePoint Online 2010 with Office 365. Unfortunately, currently there will be no way to allow for opening html files without downloading them."
The workaround suggested back then was to rename the files, replacing
.aspx, I suggest you to check if that is still a viable solution