[Bug]: New Tab Button Disappearing

[thepick]

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 tried to create 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 this problem is not ocurring in the latest version of Firefox ESR.
• This issue is specific to this browser and does not occur in other browsers.

Bug Summary

When using vertical tabs, the new tab button (when toggled on) disappears upon browser restart

Reproduction Steps

1. Go to Settings ---> Design ---> Vertical Tab bar (experimental) ---> Show the "Open a new tab" button inside Vertical Tab Bar
2. Toggle the switch on
3. Restart the browser

Expected Behavior

The button will stay visible

Actual Behavior

The button disappears

Screenshots

Browser Version

11.13.2 (64-bit)

Operating System

Windows 11

Additional Context

When the button is there, it's not centered anymore; It's sitting on the left.

[TheChilledBuffalo]

I have found the fix and will commit the changes soon.

Also, adding an appropriate title for the issue would be really helpful. Thanks!

[surapunoyousei]

It maybe my mistake...