Having a little programming knowledge (c#), I tried to change the version of the embedded web browser control, but I just couldn't find a way to do it.
Setting feature_browser_emulation was the obvious choice, but sadly had no effect.
Maybe webbrowser control is created from another layer inside RSSOwl.exe that makes this change fail.
I tried to find a way to pass some kind of parameter to either RSSOwl (through RSSOwl.ini) or to java, but my lack of java knowledge must be preventing me from finding a solution if it exists.
The number of sites saying that you have an outdated version of browser is increasing, and let's not fool ourselves, the newer sites don't display correctly using IE7 rendering.
So, please inform us if there is a way to change the version of the embedded IE browser and how to do it.
If such a feature is not yet implemented, then please consider adding it to RSSOwl for windows.
Ideally using a program setting than changing something in the OS, as Microsoft has a bad habit of changing things without caring for developers and users.
Speaking from personal experience there are a number of ways to change the rendering version of the web browser control that you use in a form. You can use feature_browser_emulation in registry (for example, FeedDemon uses this approach), or you can even add/change x-ua-compatible meta before you render the contents of the web browser control. And if you choose to do it using the x-ua-compatible approach, then you can really have a new (and completely unique as far as I know) program feature like changing the browser rendering version for specific feeds.