Faerie Fire should provide advantage universally, yes. If it isn't, that's a bug.
One thing that the game seems to be stumbling over at the moment is the requirement that you not be at disadvantage for sneak attack; If you have an ally within 5 feet, threatening he target, and you have Disadvantage from poor light, but Advantage from being unseen yourself, then you are NOT at disadvantage; you have a flat roll, and you have an threatening ally, so Sneak attack is *Valid*. However, in the game's logic at the moment, ANY instance of disadvantage knocks out Sneak Attack, even if it is being cancelled out by advantage. This is an error in the game logic that we hope will get fixed... but it's worth reporting formally when you can.
Edit: Faerie Fire is particularly nice in something similar to the example above because as well as providing Advantage in and of itself, it also causes the target to shed light - enough to see by - which means that IF you were at disadvantage from poor light, it would also remove that, as well as giving you natural advantage. At least, that is how it should work.
Last edited by Niara; 18/07/21 04:25 AM.