@ajqtrz Yep we all know the "rule", but that doesn't change the fact that "an FS" both looks and sounds wrong to many because we don't see "FS" we see "Fellowship"
So the sound of FS is actually not "eff" like it would be if we were discussing an FBI agent.
a FS (seen and pronounced: a fellowship)
an FBI agent (seen and pronounced an eff bee eye agent)
Normally this isn't the case. For example: if we are discussing "an MMO" there is no problem because you do not see "Massively Multiplayer Online (Game)"
Basically, FS acts more like an acronym than an abbreviation like how we say a MADD member
The true beauty of English is that all of its rules seem made to be broken.
Do you say, internally, when you read, MADD, "Mothers Against Drunk Driving" or "MADD" (like the word "mad"). If you say or hear the first then MADD is an abbreviation. If you say the second it functions like a synonym. The difference between an abbreviation and an acronym is that an abbreviation is a shortened representation of a word or phrase that can be shortened in many ways while an acronym is a specific way of shortening that word or phrase. Acronyms are, therefore, a subset of abbreviations. Synonyms are words in themselves representing an idea. So once people become accustomed to seeing "MADD" in places where "Mothers Against Drunk Drivers" could be written, and once "MADD" is so well known that there is no need to write "MADD (Mothers Against Drunk Driving)" MADD becomes just another name for the organization and it's role as an abbreviation becomes less and less important.
More to the point, as my last post indicated, the mental process a person goes through when reading is heavily influenced by his or her learning style (kinestetic, auditory, visual) and/or left/right brain dominance. I am an auditory reader and read the "words" without "populating" the abbreviation. Instead, I "hear" the letters. So I "say" to myself "eff ess." This internal sound is a metonym to me -- as all abbreviations are since they are a contracted representation of something else -- and as such, depending on the reader, may or may not need to be expanded into the word or phrase for which the "fs" stands. In the case of "fs" it's a metonym for "fellowship" and I do not therefore say "fellowship" to myself since to do so would be internally repetitious. After all, it wold be silly to say something like, and FBI Federal Bureau of Investigation agent" unless you indicated the "Federal Bureau of Investigation" part was a parenthetical remark by putting it into parenthesis -- to let the reader know you were expanding the acronym "FBI" in case they didn't know the source of the acronym and for what it stood. The key is to understand that some acronyms or abbreviations become metonyms and when they do they no longer function as abbreviations (though they are formally still recognized as such, of course) but as metonyms.
Having said that, the thing to understand is that sometimes the abbreviation becomes so ingrained no expansion is necessary and it takes the place of the actual thing for which it stands. Almost nobody, internally speaking, expands FBI to "Federal Bureau of Investigation" because "FBI" has become fully synonymous with "Federal Bureau of Investigation." For this reason you NEVER hear or see, "a FBI agent" but always "an FBI agent" but also never see "an Federal Bureau of Investigation agent" but always "a Federal Bureau of Investigation agent" -- if you even seen the full name used at all since "FBI" is a full synonym for Federal Bureau of Investigation.
All of which is relevant because "fs" in this game is somewhere along the process of becoming a full synonym for "fellowship" and may have arrived at that state in the minds, like mine, of some. When, and if it ever does completely transform from an abbreviation to a synonym, "a fs" will sound ungrammatical to almost everyone and "an fs" will sound correct." The only caveat is that auditory learners and left brain dominant people will tend to react to "a fs" as ungrammatical sooner than visual learners and right brain dominant people. Neither are really wrong as language is evolving -- or more correctly, changing.
In grammar there is not right and wrong, just expectation and dissonance..
At least that's how I think about it.
AJ