Ok so I know it's a pretty minor thing, but I hate the fact that you have to click the game canvas to give it focus before you can start playing. It turns out that it's not actually necessary though, you can program your game so it automatically wrests the focus into its clutches after it's loaded and flips the bird at the main browser window.

In Godot I did it with this code

	if OS.has_feature('JavaScript'):
		JavaScript.eval("document.getElementById(\"canvas\").focus();")

and in most other game engines if you can run JavaScript (see this post for an example of how to run JavaScript from Unity) then you can do this by looking through the .html file that your engine generates for an element similar to the "canvas" element that Godot makes and use its ID in the getElementById().focus() call.

I also did it in HaxeFlixel where it's even easier, just slap this code in

Browser.window.focus();

I put it in the Main.hx file's new() function just before the addChild(new FlxGame)