Mute Tab button too big on Pinned Tabs

### Describe the bug

Hi!

The Mute Tab button is a bit obtrusive in pinned tabs, as they take a lot of space, making it hard to click to open the tab.



Would it be possible to make it smaller? :)

Many thanks!

### Expected behavior

_No response_

### Screenshots

_No response_

### OS

Windows 11

### OS - Others

_No response_

### Firefox Version

132.0b5 (64-bit)

### Distribution

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

### Theme

- [ ] Light
- [ ] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [X] 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

_No response_

### `user.js` setup

user.js setup is just the default - no changes

### Additional context

_No response_

Start by locating the SCSS rules controlling the Mute Tab button in pinned Firefox tabs, then reproduce the layout shown in the issue on Firefox 132. Verify that the button occupies less space without preventing mute or tab-opening interactions, and check the result against the supplied screenshots.

Written by the indexing model from the issue text.