mobile-config-firefox/chrome/disable_newtab_on_middle_click.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/disable_newtab_on_middle_click.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* Prevents middle-clicking in empty area in tabs toolbar from opening new tabs */

#tabbrowser-arrowscrollbox{pointer-events: none}
.tabbrowser-tab,
#scrollbutton-up,
#scrollbutton-down,
#tabs-newtab-button{pointer-events: auto}