CyberGene How can the composer page be closed on mobile?
There isn't really any way to close it. You can navigate to another page using the hamburger menu.
When doing so the composer remains active but minimized and can be permanently closed while minimized. If I think of an elegant solution I'll implement it but I don't really have any good UX idea at the moment.
CyberGene Is it possible to also use the composer page for replies?
No and it's not a feature I had planned.
Currently the Composer Page doesn't include a preview so this would seem like a significant downgrade when replying.
If your audience is primarily on mobile, my extension might be of little use since the default Composer can already easily become full-page on mobile.
Sponsored features always welcome though!