FireFox userChrome.css changing url bar and tabs sizes to minimum. to find userChrome.css location go menu->help->more troubleshooting informatio->profile directory click open. Create chrome folder with file named userChrome.css. Enabling userChrome.css file support type about:config toolkit.legacyUserProfileCustomizations.stylesheets to true.

userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

/* ROOT - VARS */
*|*:root {
 --tab-min-height:      30px !important; /* adjust */
 --tab-min-width:       30px !important; /* adjust */
}

/* TABS: height */
#tabbrowser-tabs,
#tabbrowser-tabs > #tabbrowser-arrowscrollbox,
.tabbrowser-tabs .tabbrowser-tab {
  min-height: var(--tab-min-height) !important;
  max-height: var(--tab-min-height) !important;
}

#urlbar,
.searchbar-textbox {
  font-size: unset !important;
  min-height: 24px !important;
}

#identity-box {
  max-height: 22px;
}

#nav-bar .toolbarbutton-1 {
  padding: 0px !important;
}

/* Compatibility with auto-hide.css */
#navigator-toolbox {
  --nav-bar-height: 31px !important;
}