It's any acronym that's often used when someone wants to point out that a question could have been answered by reading the fine article that is being discussed. TFA = The F'ing Article.

The f...ine article

I think the abbreviation was (and probably still is) popular on Slashdot

Or, more kindly, the featured article.

Others have explained, but here is the history:

https://en.m.wikipedia.org/wiki/RTFM