Confusion with literacy?

[Adam]

I saw on twitter that someone created a post about a First Person Shooter game and they wrote:

"here's a FPS game to try out"

Now, I thought that it would of been "AN FPS" not "A FPS" as this is like saying "a orange" and not "an orange"

Is it different in this case because the abbreviation for FPS is "First Person Shooter" so "A First Person Shooter" would be correct and not "An First Person Shooter"

[Bilbo]

Always tricky - but if you are expecting people to read your abbreviation
as Eff-Pee-Ess, then 'an' is the correct form.

[Ted C]

An is used in front of a vovel sounding letter, otherwise A - an apple, a banana, an hotel, a house. Speaking it would be "an FPS" but reading it would be "a FPS", I suggest.

[Mark]

"An FPS" is correct, but whoever said correct grammar is used on twitter?