Indeed, Tranquility kind of follows the path Linux folks took by choosing the name Epiphany.
I can assure you that from the mentioned examples of Epiphany, Opera, Firefox and Chrome, Epiphany is the weakest for non-native speakers (I'm one of them).
The other names still offer a comprehensible, strong, pleasant and broad enough 'palette' of other associations to this group of people.
For example Chrome is good, everybody loves shiny things, chrome keeps out rust, signifies newness and so on.
Opera visually is the impressive highpoint in a solo brought with much skill, emotion, tonal perfection and theatre filling volume.
With Firefox it's even easier: probably anything with 'fire' in it is ferocious and the whole world knows the fox as a shrewd animal.
And Epiphany? I'm not ashamed to admit I even had to look up its meaning.
The more universal word for tranquil could be 'peace', consider what an instant ring that word has around the world! (Mind you, I'm not saying 'Peace' would be a good name for a browser here...)
What I also don't like is the reinforcement Tranquility has of the Japanese/Eastern/Zen cliché visual image of 'the old monk meditating alone in his remote ancient temple surrounded by mountains shredded in morning fog' etc...
When you look at Haiku's themselves, they can be funny, disquieting, deeply human, honest, sad, joyful and a lot more...
What tranquility does have to do with Haiku's is that Haiku's probably are born in a tranquil environment...but that's a secondary association to their actual content and character.
This secondary aspect of it leads to the marketing (in the bad, superficial sense of the word) taste of the name.
As a last remark: you talked about 'a smooth, fast and fun process'. I don't want to be word-picking but tranquil and fast aren't related per se, they can easily be each other's opposite as well.