Make firefox tabs shrink rather than scroll

In about:support

open profile folder

make a new folder called chrome

put in userChrome.css

#tabbrowser-arrowscrollbox::part(scrollbutton-up),
#tabbrowser-arrowscrollbox::part(scrollbutton-down) {
    display:none !important;
}

.tabbrowser-tab {
    min-width: initial !important;
}
.tab-content {
    overflow: hidden !important;
}

Set preference in about:config:

toolkit.legacyUserProfileCustomizations.stylesheets

to true

Source: https://superuser.com/questions/1749962/firefox-how-to-have-very-small-tab-size-and-no-tab-scroll-buttons and reddit