By now it’s a widely known fact that the browser is based on the Gecko engine which is developed by Mozilla corp. and is used in their Firefox browser and Firefox OS. For some reason it’s not that known that the Sailfish browser is built upon the EmbedLite embedding API (also known as IPCLiteAPI) for Gecko.
This embedding API started as a research project in Nokia by Oleg Romashin and Andrey Petrov at the times when Nokia was still developing the Maemo platform. Currently the project is maintained by Tatiana Meshkova.
Now it’s open sourced, so it’s for you to just jump into coding bits and bytes.