joining windows forms

i was wondering how chrome and firefox uses two windows and joins them a runtime, i have seen it done in some projects but have never played the the code myself had no use of it til this point in my project, if anyone has the resources, websites etc that they have links for i can figure it out for myself. thanks in advance.

for example:

i am making one windows forms for the tabs, the other for the webbrowser controls, i.e back buttons etc.