Ranked in these QuestionsQuestion Ranking
Pro Free, open source and community driven
Pro Functionality can be extended with add-ons
By far the best browser if not using an adblocking app like AdAway or Adguard. Adblocking, Privacy, Themes/Stylish, etc. Add-ons make Firefox the best total package mobile browser... You may even forget you're using a mobile browser.
Pro Ethical and pragmatic company mission
The Mozilla Manifesto outlines the company's mission and principles. Paraphrasing, they want the Internet to be a free and open resource, and to enable individuals to get the best use of that resource. They do this by creating open source software to which anyone may contribute, so long as such contributions fit with their principles (both ethical and technical).
Pro Built-in reading mode
Reading mode allows removing everything on a page but the text. It removes ads, styling and anything else that could get in the way of a comfortable reading experience.
Pro HTML5, mobile video support
Firefox for Android supports HTML5, and with support for multiple video formats, you can watch videos right in the browser.
Pro Great efficient and intuitive UI
The scrolling and response is generally faster than Chrome on my Android devices.
Pro Sync with desktop browser
Keep track of all your bookmarks, passwords, open tabs, and history on the go.
Pro Built-in ad blocker
Con Can't play flash videos
Due to security concerns, Firefox does not include Flash support by default.
Con Reading mode removes some images and videos
Reading mode removes non-textual elements that are not part of the article, but it retains images and videos that are part of the feed node (rss).