create custom_default_tab_favicons.css

chrome/custom_default_tab_favicons.css

@@ -0,0 +1,23 @@
+/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/custom_default_tab_favicons.css made available under Mozilla Public License v. 2.0
+See the above repository for updates as well as full license text. */
+
+/* Icon files not included. Save the icon files to same folder where userChrome.css is */
+
+ /* Default tab favicon, the globe kind of thing */
+.tab-icon-image:not([src]){
+  background-image: url("icon.png"); /* filename for icon to load */
+}
+
+/* The Firefox brand icon seen on newtab page etc. */
+.tab-icon-image[src="chrome://branding/content/icon32.png"]{
+  background-image: url("icon.png"); /* filename for icon to load */
+}
+
+/* This just set size & properties for the icon replacement */
+.tab-icon-image:not([src]),
+.tab-icon-image[src="chrome://branding/content/icon32.png"]{ 
+   background-repeat: no-repeat;
+   background-size: cover; 
+   height: 0; 
+   padding-top: 16px
+}

html_resources/tagmap.json

@@ -128,5 +128,6 @@
 "non_floating_sharp_tabs.css":["tab","proton","buttons"],
 "autohide_main_toolbar.css":["toolbars","autohide","nav-bar"],
 "sharp_menupopup_corners.css":["popup","menu","proton"],
-"overlay_tab_audio_icons.css":["icon","tab"]
+"overlay_tab_audio_icons.css":["icon","tab"],
+"custom_default_tab_favicons.css":["tab","icon"]
 }

tags.csv

@@ -128,3 +128,4 @@ non_floating_sharp_tabs.css,tab,proton,buttons
 autohide_main_toolbar.css,toolbars,autohide,nav-bar
 sharp_menupopup_corners.css,popup,menu,proton
 overlay_tab_audio_icons.css,icon,tab
+custom_default_tab_favicons.css,tab,icon