Breeze от KOPRajs

Put this to your profile/chrome/ folder, if you want the buttons and tabs radius to match Breeze as well:

// userChrome.css
:root {
--border-radius-medium: var(--border-radius-small, 5px) !important;
--tab-border-radius: 5px !important;
--button-border-radius: 5px !important;
--toolbarbutton-border-radius: 5px !important;
}

// userContent.css
@-moz-document url-prefix("about:"), url-prefix("chrome:") {
:root {
--border-radius-medium: var(--border-radius-small, 5px) !important;
}
}

@-moz-document url(about:newtab), url(about:home) {
.top-site-outer,
.top-site-outer .tile {
border-radius: 5px !important;
}
}