@yavuz

You can just click the reply button below a post to reply to someone in the browser. It works pretty much the same as the app.

I've attached a screenshot.

The dialogue box you're seeing is probably because you've opened a post on a remote site instead of within your own server's browser interface. If you log in through your server (which for you is https://geveze.social) you will be able to reply just like on the app.