Browsers aren't really feed aggregators or feed readers. There are specialized software like FeedDemon or web services like Google Reader that will let you set your preferences for feed display and reading.
In a browser you're a bit more limited in your options. If you really want to get into control of how a browser might display your feed content then you need to look into XSL Transformations (XSLT).
As far as full feeds are concerned, if you're talking about other people's feeds, then you really can't control much. Whether a full feed is offered is the choice of person generating the feed. If they choose to offer snippets with links then you are stuck with that.
If the RSS entry is showing up as a snippet with a link, and you control the feed, then you're simply not publishing a full feed. The browser won't truncate a feed. It just displays the XML it is given.