What is better to use in browser-based multiplayer games.Will Mirror do ?
It depends on your project goals.
For player-hosted games or for smaller game server instances with 10-30 players using Mirror should be totally fine.
If you need big authoritative servers with 100-1000 players (or even more), you should consider creating a custom WebSocket-based networking solution.
For early server prototyping you can use something like websocket-sharp if you plan switching to a custom solution later. Just keep in mind that it’s barely maintained and not suitable for a production server without modifications.
For the client you can use NativeWebSocket. It’s very simple and should work right out of the box.
Another sidenote:
Be aware that WebGL games in Unity are a lot less trivial to create than standalone games and that the whole WebGL build target comes with many challenges and limitations.
Thank you very much !