When comparing Fira Mono vs Monoid, the Slant community recommends Monoid for most people. In the question“What are the best programming fonts?” Monoid is ranked 19th while Fira Mono is ranked 51st. The most important reason people chose Monoid is:
The user can adjust letter-spacing, line-height, and choose alternate characters prior to downloading.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Looks great and is easy on eyes
Almost looks like Source Code pro and works great with Intelli J where Source Code Pro renders all junk on one of the primary IDE.
Very good for people who read code through out the day.
Pro Extremely readable
You can look at the code for hours and hours. The height between lines and the spacing is perfect.
Pro Offers better performance in some Emacs builds
This font is used by some Emacs users on Mac OS X in order to get better performance.
Pro Customisable
The user can adjust letter-spacing, line-height, and choose alternate characters prior to downloading.

Pro Novel use of ligatures to display ascii character combinations as symbols
The common expression '!=' is displayed as '≠', '>=' as '≥' *, while maintaining the fixed width double-space that these characters would normally take, so as to maintain text alignment.
- Many others are supported too - see site for details.
Pro Open source
Monoid is open source meaning it's freely available to anyone.
Pro Sharpness
Pro Larger and easier to read with thin condensed letters
Pro Fine without retina
Probably the only one that is.
Cons
Con Large line height
Compared to other options, Fira has a high line height, which reduces the number of lines you can see on screen at one time.
Con Very narrow
Con No bold-italic style
Monoid doesn't offer a style that is both bold and italic.
