How web browsers use process & Threads
Firefox Vs Chrome

Treads are the way for a program to divide it self into two or more simultaneously running task.In the web browsers tread is contained inside a process and different treads in the same process share resources.But the main goal is to keep the main thread and IO tread responsive.

Now we look how use this technology in the Chrome and the Firefox.

In chrome, each and every tab you open gets its own content process.If you open 10 tabs then its run in 10 processes.In this way we can get best performance but the problem is when its applicable its consume the memory and power. But Firefox does not do that.In the Firefox ,first 4 tabs each use those 4 processes, And the other tabs(threads) run in that processes.
In 64-bit mode Chrome use 1.77x more RAM than Firefox and In 32-bit mode its going to 2.44x .
Benefits
* Responsiveness: Multitheading an interactive applications may allow a program to continue running even if part of it is blocked or is performing a lengthy operation.
* Thereby increasing responsiveness to the user.
Ex:- A Multithreaded web browser could allow user interaction in one tread while an image was being load in another thread.