The previously enabled theme is not restored if the “Undo” button is clicked

[tomariana]

[Affected versions]:

• Firefox Release 94.0.1 - Build ID: 20211103134640
• Firefox Beta 95.0b10 - Build ID: 20211121185651
• Firefox Nightly 96.0a1 - Build ID: 20211123094249

[Affected Platforms]:

• Windows 10 x64
• macOS 11.6
• Linux MX-21

[Prerequisites]:

• Have a Firefox profile with the latest version of the “Firefox Color” addon installed from here (version 2.1.7).

[Steps to reproduce]:
Open the browser with the profile from the prerequisites.
Click the “Firefox Color” toolbar button.
Click the “Preset themes” tab and select any theme.
Click the “Undo” button from the top-right part of the page.
Observe the behavior.

[Expected result]:

• The previous theme is applied.

[Actual result]:

• The theme is reverted to the colors set in the “Custom colors” tab.

[Notes]:

• The issue is also reproducible if, in step 3, the change was made from the “Custom colors” tab instead of the “Preset themes” one.
• The issue is not reproducible if the “Revert All” button is clicked instead. In this case, the previous theme is restored.
• Attached is a screen recording of the issue.