Sane people might recognize that... as a spelling error, dummy. Somebody who can't keep a temper tantrum, bullies, shouts, attacks, sound like a spoilt Kid... and keeps yelling CAP LOCKS... are you sure you ain't Donald... doing a little trolling from the bunker?!
What is the best move after F4 in the bird's opening? (as white)

English is not even my native talk. for gawds sake. And rather a stuffed lion than your large M... which could stand for many things.

English is not even my native talk. for gawds sake. And rather a stuffed lion than your large M... which could stand for many things.
You can't read either!
There is no M. It is an N and a Y, and is the logo for the New York Giants!
You just keep digging that hole deeper.

I have found d5 to be a good one. Often with Bg4 early and Nd7 with e5 if possible.
That system is weak, and the e5 gambit is unsound.
1.f4 d5 2.Nf3 Bg4?! 3.e3 Nd7 4.h3! Bxf3 5.Qxf3 and if ...e5, the d-pawn hangs.
Nothing like missing the point. See the red highlighted text,
The sequence is still valid and is a major method of dealing with the Bird's. In the event of your line above, 5...c6 would be just the thing to stop calamity. Ngf6 also works.

I have found d5 to be a good one. Often with Bg4 early and Nd7 with e5 if possible.
That system is weak, and the e5 gambit is unsound.
1.f4 d5 2.Nf3 Bg4?! 3.e3 Nd7 4.h3! Bxf3 5.Qxf3 and if ...e5, the d-pawn hangs.
Nothing like missing the point. See the red highlighted text,
The sequence is still valid and is a major method of dealing with the Bird's. In the event of your line above, 5...c6 would be just the thing to stop calamity. Ngf6 also works.
5....e5 is a line, and a gambit, but it's unsound.
5...Ngf6 allows the dangerous "Bayonet Attack", which is 6.g4! Tim Taylor does excellent coverage of this line in his book on Bird's opening.
He even mentions in the book Black's best defense and move order. 1...d5 (to avoid early e4 lines) and then either 2...g6, 3...Bg7, 4...Nf6, 5...O-O, and 6...c5 if he wants to avoid the b3 lines, and 2...Nf6, 3...c5, and 4...Nc6 if he wants to avoid the Antoshin as 5...d4 is very strong in that line (1.f4 d5 2.Nf3 Nf6 3.d3 c5! 4.c3 Nc6 5.Qc2?! d4!). The Antoshin should really only be played against the early fianchetto.
But what he calls "The Recipe" is dubious because of the Bayonet Attack, and the gambit line with 5...e5 is also not sound as he does not get the proper comp after the Queen takes the d-pawn.

I see nothing wrong with 1...e5.
And in the main line 2.fxe5 d6 3.Nf3 dxe5 4.Nxe5 Bd6 5.Nf3, 5...g5 is a good alternative to the standard 5...Nf6, despite of what most people think.
Nobody plays Bird opening, braw. Not seriously. If a super GM don't play, a patzer don't play.
You have no clue what you are talking about lowly 1600 player.
We have 3 titled players right now playing in 2020's 4th thematic (of 7) at the ICCF. What is that thematic? Bird's Opening! 1.f4, Black to move in every game.
Shut up, you lowly 1900. I'm leaving this I just had to roast you

I see nothing wrong with 1...e5.
And in the main line 2.fxe5 d6 3.Nf3 dxe5 4.Nxe5 Bd6 5.Nf3, 5...g5 is a good alternative to the standard 5...Nf6, despite of what most people think.
3.Nf3 is not the main line. The main line is 3.exd6.

@thrillerfan... Check again bro. Not a letter y. Or Y. Dummy.
Then what the hell do you call the second letter here if it's not a y? Don't be telling me I'm wrong when you aren't even from this country and clearly have no clue about logos!

I see nothing wrong with 1...e5.
And in the main line 2.fxe5 d6 3.Nf3 dxe5 4.Nxe5 Bd6 5.Nf3, 5...g5 is a good alternative to the standard 5...Nf6, despite of what most people think.
3.Nf3 is not the main line. The main line is 3.exd6.
It's the very same position after 3.exd6 Bxd6 - in my case with 2 extra moves played for both sides. Black has nothing better than transposing to that line after 3.Nf3.

Nobody plays Bird opening, braw. Not seriously. If a super GM don't play, a patzer don't play.
You have no clue what you are talking about lowly 1600 player.
We have 3 titled players right now playing in 2020's 4th thematic (of 7) at the ICCF. What is that thematic? Bird's Opening! 1.f4, Black to move in every game.
Shut up, you lowly 1900. I'm leaving this I just had to roast you
You will soon wish you never said that!

@thrillerfan... Check again bro. Not a letter y. Or Y. Dummy.
ny. the y is extended.

Let's get back on topic, though. ...g5 is discredited, while I believe ...Nf6 leads to weirder play.
Nobody cares, sir.
Look, someone posted the question and I answered. You and your snide BS remarks are not to be tolerated. Keep it up and I am reporting you.
If you have something USEFUL to say, we will be glad to hear it. If all you are going to do is attack other posters, SHUT UP NOW!
Maybe if you would quit YELLING like a DUMB pathological BUFOON... you wouldn't get a negative reaction, hmm? Nobody is caring if you play Classical Bird, Orangutang Bird or Dodo Bird... not a great opening. Probably, you like the Grob as well.
All you are doing, as pfren mentioned, is dying for attention. You sound like a complete fool doing it too.
BUFOON??? WHAT IS THAT???
I know what a BUFFOON is! Definition? An uneducated person that can't spell and posts nothing on chess.com forums other than attack posts to try to grab attention and has a stuffed lion as a logo.