After many years, Mozilla has finally started testing their new and improved Firefox web browser in their latest nightly build.
I decided to try it out after Nate Brune( 
The updated UI brings a new look and the ability to change the theme of the browser. The overall performance is faster and by default, Multi-Process is enabled.
It's been a while since I used Firefox but I don't recall it having a screenshot tool enabled like you see on the top right corner of the browser.
With Multi-Process enabled, this should improve overall performance and stability. The thing with this is that each process contains an instance of the browser's rendering engine and become a memory hog like the Chrome browser. Mozilla said they have worked on reducing the memory consumption and you only get four content processes by default. That is the apparent sweet spot to not use too much RAM and utilizing the multi-core CPUs.
You are able to change this by typing about:config and tweak dom.ipc.processCount in the address bar to increase the content process but this will also increase memory usage. This is why Chrome browser tends to use a lot of memory because it starts a new process for every tab.
Mozilla created project Stylo to build the next generation web engine for Firefox and is built on the Gecko engine.
PSA on reddit:
Stylo is the project to take Servo's style system and put it inside Firefox. It uses Rust and does styling in parallel, which makes it both more secure and fast.
As of two weeks ago, we've been shipping it in Firefox Nightly (desktop), disabled by default.
If you want to run more Rust code on your machine, or help this project along, download Nightly and flip the pref layout.css.servo.enabled in about:config. I've personally noticed that stuff is much smoother/faster on many sites, and never perceptibly slower on others.
If you would like to give it a try, visit:
https://www.mozilla.org/
