Does what it says. Thank you, TaYaKi71751.

You can fix the tab icon using userChrome.css. Put the icon image (google it) in the directory with your userChrome.css file. There may be a better CSS selector combo, but I found this through some trial and error and it seems to work fine.

/* restore old twitter logo in tabs */
.tabbrowser-tab[label*="/ Twitter"] .tab-content .tab-icon-image {
content: url("Logo_of_Twitter.svg") !important;
}