Gecko is the rendering engine for Firefox. Using gecko-sharp it is possible to embed it to any Mono/GTK# program. There is a sample application called GladeSharpBrowser for doing this. I could manage to build it using a modified project file, but it is crashing. This sould help you reproduce the problem:
I have used SharpDevelop 3.0 and a tutorial to set it up with my Mono 2.2 installation. I have made sure it calls Mono's gmcs for compilation using ProcMon. After setting up SharpDevelop, the BrowserSharp.csproj had to be modified so it compiles with Mono.
There is also a warning message:
Found conflicts between different versions of the same dependent assembly.
This is strange, since all the assemblies are the ones provided by Mono.
Sure, there are other methods like GeckoFX, but I am specifically interested in doing it in a platform independent manner using Mono.