New(ish) Compose Box overflow scrolls horizontally with 4 columns in advanced interface

[midnightveil]

Steps to reproduce the problem

1. Enable advanced interface
2. Pin another column, so that there are 4 columns
3. Notice now that the compose box overflows horizontally

Expected behaviour

No horizontal overflow (like it used to, before the compose box updates)

Actual behaviour

It overflows :(

Detailed description

Enabling 'Always enable the Content Warning field' or disabling 'Show content-type choice when authoring toots' makes the overflow go away.

I expected this to be an issue with my instance's higher character count, but even with the default 512 count this is an issue.

Everything other than as mentioned is the default, I just spun up an instance to test.
Devtools show that the viewport is 1760px wide by 866.25px tall.

Mastodon instance

localhost

Mastodon version

v4.3.2+glitch (c2d65f7)

Browser name and version

Firefox 133.0 (64-bit)

Operating system

Linux/Fedora 41

Technical details

No response