Wrong icon style in Firefox sidebar

[scheinercc]

Describe the bug While the topbar shows the STG extension icon in the selected style, the FF sidebar shows the default icon instead.

To Reproduce Steps to reproduce the behavior:

1. Go to STG Settings > General
2. Click on "Default group"
3. Set icon style

Expected behavior Selected icon style used in Firefox topbar as well as sidebar.

Desktop (please complete the following information):

• OS and version: macOS 14.5
• Firefox version: 130.0b3
• Simple Tab Groups version: 5.2