UI cut when in Firefox overflow menu

[rugk]

Describe the issue

Similar to #2809, but quite the opposite: When in the overflow menu, uBlock origin has a too big width.

One or more specific URLs where the issue occurs

Everywhere.

Screenshot in which the issue can be seen

Steps for anyone to reproduce the issue

0. Enable expert mode or so, the "default" UI is small enough.
1. Move icon into overflow menu.
2. Open it.

Potential solution

Either:

• Make UI somehow "responsive".

Or:

• Enable horizontal scrollbar, there, so you can scroll, at least.

Versions

• Browser/version: Firefox 58
• uBlock Origin version: uBlock Origin 1.15.10

Your filter lists

do not matter

Your custom filters (if any)

do not matter

[myspaghetti]

Reproduced in Firefox 59.0.2 on Windows 10, uBlock Origin 1.15.18

[gorhill]

Duplicate of #2809.