When comparing Opera Mini vs Firefox android, the Slant community recommends Opera Mini for most people. In the question“What are the best mobile browsers ?” Opera Mini is ranked 7th while Firefox android is ranked 10th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Completely free
Pro Very light weight
Great for phones with lower RAM or performance issues.
Pro Has built-in ad blocker
Pro Has a data saver
Opera mini's data saver has two modes - regular and extreme. great for people with smaller data plans when not on wifi. Has also the ability to control the quality of downloaded images and some video optimizations.
Pro Optimized for Facebook
Pro Tracking protection
The built-in tracking protection can improve page load speed.
Pro Privacy focused
Pro Addons on mobile version
Supports addons like ublock-origin, privacy badger and many more like it's desktop counterpart
Pro Reader mode
Using reader mode on supported webpages improves reading experince
Cons
Con Doesn't support some common modern browsers functionalities
Some web pages might look a bit broken but from personal experience it doesn't happen often enough (or at all) to be a major issue.
Con Many bugs
In extreme data saving mode, it sometimes won't load page correctly.
Con Has issues while playing video
It will crash when you are playing video.
Con Address bar at top
Having the address bar at the bottom helps in navigation on a big display