Backspace and delete behave incorrectly in composer when selecting quickly on Firefox

### Steps to reproduce

Attempt to type in the composer in any room.
Select all with CTRL+A or equivalent, and very quickly press backspace. Nothing will happen, and the cursor will return to the beginning of the input area

Of note, the 'delete' key works _partially_, but not as intended, and somehow differently from backspace. It will delete portions of the message, up to where spaces are present, or the whole message if there are no spaces.

### Outcome

#### What did you expect?
In both instances, the entire message should be deleted, as the entire message is selected.

#### What happened instead?
See above.

### Operating system

Windows 8.1

### Browser information

Firefox 115.12.0esr (64-bit). Not reproducible on Chrome.

### URL for webapp

https://app.element.io/

### Application version

1.11.69

### Homeserver

matrix.org

### Will you send logs?

No