I have a question related to this SSB's, how does this sort of engines actually work?? I want to try to code something similar (if possible) just for the sake of it but I have found nothing regarding their behaviour or how to start on building one.Not sure what to look for either.
You'll find a lot of resources regarding Google Gears on the official website, including the architecture and security model. You can actually check out the source code for Gears, since it is has been released under the BSD license.
Mozilla Prism is also open source, allowing you to actually look at the source code to figure out how it works. You can probably find more about its architecture on its website.
Mozilla Prism, last time I checked, is completely different to Google Gears. In fact, Google Gears is to complement apps like Prism.