Full code changes: https://github.com/Aris-t2/CustomCSSforFx/commits/

Changelog:

[userChrome.css]

• moved tab audio icon settings into own category

[Buttons]

• (tweak) more compact mode

[General UI]

• (fix) Fx 136+: sidebar show on hover
  • Fx 136 compatibility causes large visible hover area
  • Fx 128+135 code moved into sidebar_show_on_hover_fx128.css

[Tabs]

• (fix) Fx 136+: 'tab audio icon' option (thx to Speravir)
  • audio icon is slightly different compared to Fx 135
• (fix) Fx 136+: 'tab audio icon colorized' option (thx to Speravir)
• (new) hide favicon, if tab audio icon is present: tab_audio_icon_favicon_hidden.css (thx to Speravir)
• (new) remove tab audio icon: tab_audio_icon_hidden.css
• (tweak) tabs below main content

[Add-on Manager (about:addons)]

• (fix) Fx136+: alternative appearance