Cosmo Player is for viewing 3D (VRML worlds; suffix *.wrl; MIME types model/vrml and x-world/x-vrml) in browsers and can be downloaded from:
After downloading, run the installation. It will ask you whether you want to use it as a standalone browser or with other (unsupported) browser. Choose the second option (unsupported browser) and define your K-Meleon plugins directory in the installation. This should work and after that, the following files will be in your K-Meleon Plugins directory:
If they are not there, try to locate those files on your hard disk and copy them to the K-Meleon plugins folder. After that, Cosmo should work with K-Meleon.