Extension's context menu has icon/text padding issue

### Describe the bug

As in picture, click the toolbar's extension button, then click the gear icon of any extension, the icon has no padding with the text. All other menus are perfect.

I'm on latest proton and set chrome/content to monospace font.

### Expected behavior

There should be a padding between the icon and text.

### Screenshots

_No response_

### OS

Mac OS

### OS - Others

_No response_

### Firefox Version

144.0b5 (aarch64)

### Distribution

- [ ] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [ ] [Lepton's photon style](https://github.com/black7375/Firefox-UI-Fix/tree/photon-style)
- [x] [Lepton's proton style](https://github.com/black7375/Firefox-UI-Fix/tree/proton-style)

### Theme

- [x] Light
- [ ] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [ ] System Default
- [ ] Others: (e.g. [Photon Colors](https://addons.mozilla.org/en-US/firefox/addon/photon-colors/), [Google Chrome Dark](https://addons.mozilla.org/en-US/firefox/addon/google-chrome-dark/), [Fairytale Of Nature](https://addons.mozilla.org/en-US/firefox/addon/fairytale-of-nature/))

### Theme - More Info

Default theme

### `user.js` setup

user.js setup

```javascript
user_pref("userChrome.theme.monospace", true);
user_pref("userContent.page.monospace", true);
```

### Additional context

_No response_

Reproduce the issue in Firefox 144 with the proton style and monospace settings by opening the extensions toolbar menu and an extension's gear menu. Start by locating the proton-style context-menu rules; adjust the icon-to-text spacing so it matches the other menus, then verify the expected padding in the same menu on the reported Mac OS setup.

Written by the indexing model from the issue text.