Currently, all binary files are being downloaded in the browser because the Content-Disposition header is set to "attachment". A developer should be able to modify this globally and per MIME type.

In eZ Publish legacy, there are settings for this:

https://github.com/ezsystems/ezpublish-legacy/blob/master/settings/file.ini#L99

In eZ Platform, we have this bundle from Contextual Code, but it should be part of the core:

https://ezplatform.com/packages/contextualcode-ezplatform-content-disposition-bundle