I have to retract the opinoin above, because after I had permanently installed Waterfox, at some point I had to install the banking routine on it. That is a very easy task in Firefox, but the banking software refused to accept Waterfox's much stricter privacy protection. No matter what I changed regarding privacy settings, nothing helped. Ultimately, I decided not to make Waterfox permanent after all and stuck with Firefox. Because my thoughts were: what if other sites do not accept this much more strict privacy settings? With Firefox I know I don't have any problems with any sites at all...
I have then heavily modified Firefox using userChrome.css and userContent.css files (the latter for the about:... pages such as about

references). I spent well over two weeks working on it and I am very satisfied with the result. This is the way Firefox 158 now is looking:
View attachment 186647
No trace of Nova at all, back to what it was!
I learned a lot about the structure Mozilla uses these days for coding the UI of Firefox. Knownow that the code in te userChrome has to be according to that newer codes of Mozilla.
An example:
All popup panels, menus and so on are coded for corner radius ans colors in this way:
panel,
dialog,
findbar,
form,
#searchFilter {
/* border-radius changes*/
accent-color: rgb(0, 114, 240) !important;
--badge-border-radius: 4px !important;
--button-border-radius: 4px !important;
--border-radius: 4px !important;
--border-radius-small: 4px !important;
--border-radius-medium: 4px !important;
--border-radius-large: 4px !important;
--border-radius-xlarge: 4px !important;
--border-radius-circle: 9999px !important;
--button-border-radius: 4px !important;
--card-border-radius: 4px !important;
--card-border-radius-compact: 4px !important;
--card-cover-image-border-radius: 4px !important;
--input-search-border-radius: 4px !important;
--input-text-border-radius: 4px !important;
--menuitem-border-radius: 4px !important;
--panel-border-radius: 4px !important;
--panel-menuitem-border-radius: 4px !important;
--popup-border-radius: 4px !important;
--select-border-radius: 4px !important;
--toolbarbutton-border-radius: 4px !important;
/* colors changes */
--border-color-interactive: rgb(0, 114, 240) !important;
--border-color-interactive-hover: rgb(0, 114, 240) !important;
--button-background-color-hover: rgb(218, 218, 227) !important;
--button-background-color-active: rgb(200, 200, 213) !important;
--button-border-color-hover: rgb(0, 114, 240) !important;
--button-border-color-active: rgb(0, 114, 240) !important;
--button-background-color-primary: rgb(0, 114, 240) !important;
--button-background-color-primary-hover: rgb(0, 95, 205) !important;
--button-background-color-primary-active: rgb(0, 65, 175) !important;
--button-background-color-ghost-hover: rgb(218, 218, 227) !important;
--button-background-color-ghost-active: rgb(200, 200, 213) !important;
--button-background-color-menu: rgb(255, 255, 255) !important;
--button-background-color-menu-hover: rgb(218, 218, 227) !important;
--button-background-color-menu-active: rgb(200, 200, 213) !important;
--button-border: 1px solid rgb(0, 114, 240) !important;
--color-accent-primary: rgb(50, 130, 240) !important;
--color-accent-primary-hover: rgb(0, 95, 205) !important;
--color-accent-primary-active: rgb(0, 65, 175) !important;
--input-border-color: rgb(0, 114, 240) !important;
--input-text-border-color: rgb(0, 114, 240) !important;
--focus-outline: 2px solid rgb(0, 114, 240) !important;
--select-background-color-hover: rgb(218, 218, 227) !important;
--select-border-color: rgb(0, 114, 240) !important;
--select-border-color-hover: rgb(0, 114, 240) !important;
--trustpanel-background: rgba(207, 207, 216, 0.4) !important;
--focus-outline-color: rgb(0, 114, 240) !important;
--link-color: rgb(0, 114, 240) !important;
--link-color-hover: rgb(0, 95, 205) !important;
--button-border-color-disabled: rgb(0, 114, 240) !important;
}
Sometimes it is really very hard to find the right -- expression via the Devtools.
But I am glad I managed to get it this way and will stay with Firefox as long as it will exist or as long as I live, whichever comes to an end earlier...