My Firefox userChrome.css file

 @-moz-document url(chrome://browser/content/places/places.xhtml) {
  #placeContent treechildren {
    font-size: 14px !important;  /* font size in Bookmarks> Manage Bookmarks> Library popup on the right hand side */
font-family: 'Trebuchet MS' !important;
  }
}

@-moz-document url(chrome://browser/content/places/places.xhtml) {
  #placesView {
    font-size: 14px !important;  /* font size in Bookmarks> Manage Bookmarks> Library popup on the left hand side */
font-family: 'Trebuchet MS' !important;
  }
}

 /* Multi Rows in Firefox. This is the fix. Still hard to move tabs to other rows. Go slow when doing so. */
scrollbox[part][orient="horizontal"] > * { flex-wrap: wrap; }

/*  the order of the toolbars. Change to what you want */
#nav-bar {order: 1 !important}
#PersonalToolbar {order: 2 !important}
#TabsToolbar {order: 3 !important}

/* URL field text size */
 #nav-bar{
font-size: 12px !important;}

/* Sidebar Color / Font Size Formatting */
.sidebar-placesTree treechildren::-moz-tree-cell-text { font-size: 15px !important; color: #000 !important;
font-family: 'Trebuchet MS' !important;
/* font-weight: bold;  */
}

/* Bookmark folder code below from sifferedd (I changed the color using Irfanview to muted yellow  */
/* https://www.reddit.com/r/FirefoxCSS/comments/12jynm6/folder_svg_file */
/* Folder-item.png file is from https://github.com/Aris-t2/CustomCSSforFx/blob/4.4.8/current/image/folder-item.png */
/* Need folder file to be in the profile/Chrome folder */
.bookmark-item[container],
treechildren::-moz-tree-image(container),
.folder-icon {
  list-style-image: url("folder-item4.png") !important;
}

/* MediumAquamarine - green background on hover on sidebar or selected   */
.sidebar-placesTree treechildren::-moz-tree-row(hover),
.sidebar-placesTree treechildren::-moz-tree-row(selected) {background-color: #66CDAA !important; }


/* code below from sifferedd */
#navigator-toolbox {
  font-family: "Quicksand Medium" !important;
  color: #000000 !important;
}

.bookmark-item > .toolbarbutton-text {
  font-size: 14px !important;
  font-family: 'Quicksand Medium' !important;
}

#personal-bookmarks {
  font-size: 14px !important;
  font-family: 'Quicksand Medium' !important;
}

#bookmarksMenuPopup,
.bookmark-item {
  font-size: 14px !important;
  font-family: 'Quicksand Medium' !important;
 }

/* file, edit, view etc font size */
#main-menubar {
  font-size: 15px !important;
font-family: 'Quicksand Medium' !important;
}

:root {
  --tab-border-radius: 8px !important;
}

/* box-shadow: horizontal offset, vertical offset, blur radius, optional spread radius, color & transparency; */

/* White background color */
.tabbrowser-tab:not([selected="true"]):not(:hover) .tab-content {
  background-color: #ffffff !important;
  border-radius: 8px 8px 0px 0px; !important;
box-shadow: 1px 0px 1px 0px rgba(0, 0, 0, 0.4);
}

/* orange hover color */
.tabbrowser-tab:hover:not([selected]) .tab-content {
  background-color: #FF7F50 !important;
  border-radius: 8px 8px 0px 0px; !important;
box-shadow: 1px 0px 1px 0px rgba(0, 0, 0, 0.4);}


/* MediumAquamarine selected color */
.tabbrowser-tab:is([visuallyselected],[multiselected]) .tab-content {
  background-color: #66CDAA !important;
  border-radius: 8px 8px 0px 0px; !important;
box-shadow: 1px 0px 1px 0px rgba(0, 0, 0, 0.4);}


/* font size on tabs */
.tab-label {
  font-size: 12px !important;
font-family: 'Quicksand Medium' !important;
font-weight: bold;
  }


/* code from qaz69wsx */
/* font size for right click menu */
menupopup {font-size: 13px !important;}

/* font size for dropdown menu lines before bookmarks */
menubar {font-size: 14px !important;}


/* code from qaz69wsx with some changes in colors for right click menu */
menupopup:not(.in-menulist, .toolbar-menupopup, .toolbar-menupopup menupopup) {
  --panel-background: #f9f9fb !important;  /* right click menu color light grey with darker grey hover color */
  --panel-color: #000000 !important;
  --panel-padding: 6px !important;
  --panel-border-radius: 12px !important;
  --panel-border-color: transparent !important;


[_moz-menuactive]:not([disabled="true"]) {
  color: #000000 !important;  /* text color */
  font-weight: bold;
  /* also makes dropdown menu text bold when highlighted */
}

[_moz-menuactive="true"][disabled="true"] {
  background-color: #ffffff !important;
}


/* changes the menu hover color */
    menu:where([_moz-menuactive="true"]:not([disabled="true"])), menuitem:where([_moz-menuactive="true"]:not([disabled="true"])) {
    background-color: #66CDAA !important; /* green hover color */
    color: #000000 !important;  /* text color */
   /* if font-weight: bold; is added here instead of above code, the File, Edit, View etc will also be bold when highlighted and will make menu expand */
    }