[Bug]: Theme doesn't apply correctly to vertical tab bar

[TheToxicToast]

Pre-Submission Checklist

• I have checked the existing/closed issues to ensure this issue has not already been reported.
• I am using the latest supported version of the browser.
• I have tried disabling all browser extensions/add-ons to rule out interference from these.
• I have tried clearing the browser cache and cookies.
• I have checked with a new profile and the issue still occurs.
• I have provided detailed step-by-step instructions on how to reproduce the issue.
• I have included relevant screenshots or console outputs.
• I have checked that this problem is not occurring in the latest version of Firefox ESR.
• This issue is specific to this browser and does not occur in other browsers.

Bug Summary

When applying a firefox theme, the vertical tab bar does not change color correctly. It stays gray which is very ugly

Reproduction Steps

Install and apply Catppuccin Mocha - Flamingo theme

Expected Behavior

vertical tab bar also turn purple

Actual Behavior

tab bar stays gray

Screenshots

Browser Version

Mozilla Floorp 11.20.0

Operating System

Fedora 40

Additional Context

No response