Mozilla recently announced Firefox Focus, a new lightweight browser that is the perfect fit for one off session. For example a friend just sent you an article and you want to be able to quicky read it.
Focus is shipped with a native ad blocker. Load the content you are looking for, not the ads.
Focus has a single screen, no tabs. This means a faster start up. There is no need for your phone to load unrelated tabs.
Focus clears cookies and history after each session. Again this means a fresh (e.g faster) start but more importantly you are less vulnerable to a whole set of attacks like CSRF attacks. No one can trick you into sharing an article on Facebook since you are not even logged in.
What I believe will make Focus successful is that it tries to solve a very specific yet common use case: quickly open a link or perform a search. You can also safely make it your default browser as once a page is open in Focus, you can easily switch to any other browser.