Don't displayed button "dark mode"

[Yarrax]

I use redmine 4.0.5.stable. After install redmine_dark on sema desktops i can't find dark mode button:

• on my wosrkstation with centos 7 in firefox 91.10.0esr;
• on windows desktopn with firefox 106.0.5;
• on my opensuse station with firefox 100.0.2.

I disable all extensions, but has no effect. Is it a bug in plugin?