Thank you god (macha)

グーグルカレンダーの仕様変更により11月15日の七五三のようなものまで祝日判定にされている

This extension does not work on my installation of Firefox 124.0.1 (64-bit) on Windows.

FYI, in that installation I have the following extensions related to Google Calendar:
GcalColor
G-CAL Highlighter
Google Calendar Scroll Disabler
Tags for Google Calendar
Tags for Google Calendar Plus™ (disabled)

On the same computer, in Chrome I have a similar extension called G-calize installed that works correctly.

Anyway, thank you for your effort and generosity.

Thanks! Google calendar is finally usable for people who are used to Japanese style calendars! For those who say that it doesn't work with holidays, in the settings, you have to to choose a country in the list and check 'enable color'

Amazing, this is exactly what I was looking for!

Cela fonctionne mais pas pour les vacances