I solved adding the next code in userChrome.css, instead of using userContent.css, or maybe is neccessary to use both codes in each file:
:root:is([privatebrowsingmode="temporary"]) {
--tabpanel-background-color: transparent !important;
}
I solved adding the next code in userChrome.css, instead of using userContent.css, or maybe is neccessary to use both codes in each file:
:root:is([privatebrowsingmode="temporary"]) {
--tabpanel-background-color: transparent !important;
}