pin as app tab minimum width change firefox

put the following file inside your profile/chrome folder

userChrome.css



 .tabbrowser-tab[pinned] {
        max-width: 250px !important;
        min-width: 250px !important;
   min-height: 22px !important;
   padding-right: 3px !important;
   padding-left: 3px !important;
}