New Post dialog opens on Command C

**Describe the bug**
I navigate to any post and select some text to copy, then hit `Command C` on my keyboard instantly the New Post dialog pops up and obscures what I was trying to copy

I recorded a screencapture here:
https://github.com/cheeaun/phanpy/assets/7890201/9e4a87f1-806a-4333-a0b7-2764b3b617b6

- dev.phanpy.social
- 2024.04.14.06c6360
- https://social.wake.st/@liaizon

**Desktop**
- macOS 13.6.4
- Firefox
- 124.0.2 (64-bit)

**additional comments**
It doesn't do this while the reply field is open.

Reproduce this on a post with selected text using macOS Firefox, then trace the keyboard handling that opens the New Post dialog. Verify the behavior with the reply field both closed and open. Done means Command-C copies selected text without opening the dialog, while the New Post shortcut still works where intended.

Written by the indexing model from the issue text.