全部css代码:
hbox[part="innerbox"] > .popup-internal-box > .arrowscrollbox-scrollbox,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox
.scrollbutton-up.menupopup-scrollbutton + scrollbox,
.scrollbutton-up.menupopup-scrollbutton + spacer + scrollbox {
display: block !important;
column-count: 3 !important;
column-width: 225px !important;
-moz-column-width: 225px !important;
-moz-column-rule: 1px solid #ccc;
column-rule: 1px solid #ccc;
padding-top: 4px;
padding-bottom: 4px
}
/* Overall minimum width: accommodate full column count */
#bookmarksMenu menupopup,
#BMB_bookmarksPopup,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox {
min-width: calc(3 * (225px + 5px)) !important;
}
/* Subfolder minimum width: accommodate folder column count */
#bookmarksMenuPopup .bookmark-item[container="true"] menupopup[placespopup="true"],
#BMB_bookmarksPopup menupopup[placespopup="true"],
#PlacesToolbarItems .bookmark-item[container="true"] menupopup[placespopup="true"] {
min-width: calc(3 * (225px + 5px)) !important;
/* column-count: var(--foldercolumncount); */
}
/* Force item widths so each has its own line */
#bookmarksMenuPopup menu, #bookmarksMenuPopup menuitem, #bookmarksMenuPopup menuseparator,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,
#PlacesChevronPopup .bookmark-item,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
width: 225px !important;
}
/* Clean up item and separator spacing */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
padding: 0 2px 0 2px !important;
margin: 0 !important;
}
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator {
margin: 0 !important;
padding: 0 !important;
}
.subviewbutton.panel-subview-footer {
min-height: 1px !important;
border-top: none !important;
}
/* Pack more in vertically */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem {
min-height: 1.5em !important;
}
/* Remove scrolling triangles from classic menu */
#bookmarksMenuPopup .autorepeatbutton-up, #bookmarksMenuPopup .arrowscrollbox-overflow-start-indicator,
#bookmarksMenuPopup .arrowscrollbox-overflow-end-indicator, #bookmarksMenuPopup .autorepeatbutton-down {
display: none !important;
}
注:
from: https://forum.userstyles.org/discussion/79660/firefox-developer-70
这个本是70版本兼容的, 但是在72版本炸了.
经过多次尝试 发现好像是":root"这个变量空间可能被改动了
所以这里稍微改了下, 把相关的值写死就行了.
效果: 收藏夹3列模式
使用方法:
把上面的代码, 塞入userChrome.css文件, 重启firefox即可.
如果你不知道"userChrome.css"是什么,请参考以下:
https://www.userchrome.org/
http://kb.mozillazine.org/UserChrome.css

但是使用这个css以后所有的菜单都成了三列【尴尬】

76版本
/*收藏夹多列模式 start*/
hbox[part="innerbox"] > .popup-internal-box > .arrowscrollbox-scrollbox,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox ,
#scrollbutton-up[part="scrollbutton-up"] + scrollbox[orient="vertical"],
#scrollbutton-up[part="scrollbutton-up"] + spacer + scrollbox[orient="vertical"]
{
display: block !important;
column-count: 2 !important;
column-width: 225px !important;
column-rule: 1px solid #ccc;
padding-top: 4px;
padding-bottom: 4px;
padding-left: 0px;
padding-right: 0px;
}
/* Overall minimum width: accommodate full column count */
#bookmarksMenu menupopup,
#BMB_bookmarksPopup,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox {
min-width: calc(2 * (225px + 5px)) !important;
}
/* Subfolder minimum width: accommodate folder column count */
#bookmarksMenuPopup .bookmark-item[container="true"] menupopup[placespopup="true"],
#BMB_bookmarksPopup menupopup[placespopup="true"],
#PlacesToolbarItems .bookmark-item[container="true"] menupopup[placespopup="true"] {
min-width: calc(2 * (225px + 5px)) !important;
/* column-count: 3 !important; */
}
/* Force item widths so each has its own line */

#bookmarksMenuPopup menu, #
bookmarksMenuPopup menuitem, #bookmarksMenuPopup menuseparator,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,
#PlacesChevronPopup .bookmark-item,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
width: 225px !important;
}
/* Clean up item and separator spacing */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
padding: 0 2px 0 2px !important;
/* padding: 0 2px 0 2px !important; */
margin: 0 !important;
}
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator {
margin: 0 !important;
padding: 0 !important;
}
.subviewbutton.panel-subview-footer {
min-height: 1px !important;
border-top: none !important;
}
/* Pack more in vertically */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem {
min-height: 1.5em !important;
}
/* Remove scrolling triangles from classic menu */
#bookmarksMenuPopup .autorepeatbutton-up, #bookmarksMenuPopup .arrowscrollbox-overflow-start-indicator,
#bookmarksMenuPopup .arrowscrollbox-overflow-end-indicator, #bookmarksMenuPopup .autorepeatbutton-down {
display: none !important;
}
/*收藏夹多列模式 end*/
效果: 收藏夹两列模式(仅firefox76版本)
已知问题: 会影响网页页面中出现的的下拉菜单的显示.
注: 非收藏夹重度用户, 不建议使用.
顺带推一个插件:Bookmark Tab Here (效果: 右击收藏夹item/folder--显示选项--将当前页收藏到此处)

大佬厉害！

有没有检测书签是否失效的扩展或脚本呢？

针对81版本,更新了下
hbox[part="innerbox"] > .popup-internal-box > .arrowscrollbox-scrollbox,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox ,
#scrollbutton-up[part="scrollbutton-up"] + scrollbox[orient="vertical"],
/*#scrollbutton-up[part="scrollbutton-up"] + spacer + scrollbox[orient="vertical"] 2020-09-26 81版本这里是加入了一个box容器嵌套了一次..*/
#scrollbutton-up[part="scrollbutton-up"] + spacer + box scrollbox[orient="vertical"]
{
display: block !important;
column-count: 2 !important;
/* column-count: 3 !important;*/
column-width: 222px !important;
column-rule: 1px solid #ccc;
padding-top: 4px;
padding-bottom: 4px;
padding-left: 0px;
padding-right: 0px;
}
/* Overall minimum width: accommodate full column count */
#bookmarksMenu menupopup,
#BMB_bookmarksPopup,
.panel-arrowcontainer > .panel-arrowcontent > .popup-internal-box > .arrowscrollbox-scrollbox {
min-width: calc(2 * (225px + 5px)) !important;
}
/*收藏夹--文件夹--弹窗容器的宽度*/
#bookmarksMenuPopup .bookmark-item[container="true"] menupopup[placespopup="true"],
#BMB_bookmarksPopup menupopup[placespopup="true"],
#PlacesToolbarItems .bookmark-item[container="true"] menupopup[placespopup="true"] {
min-width: calc(2 * (225px + 5px)) !important;
/* column-count: 3 !important; */
}
/*收藏夹--收藏文件夹/内部对象--宽度*/
#bookmarksMenuPopup menu, #bookmarksMenuPopup menuitem, #bookmarksMenuPopup menuseparator,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,
#PlacesChevronPopup .bookmark-item,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menu,
#PlacesChevronPopup .bookmark-item > menupopup[placespopup="true"] menuitem,
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator,

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
width: 225px !important;
max-width: 225px !important; /*2020-09-26 这里修正了81版本默认值是32em的问题*
}
/* Clean up item and separator spacing */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem, #BMB_bookmarksPopup menuseparator {
padding: 0 2px 0 2px !important;
margin: 0 !important;
}
#PlacesToolbarItems .bookmark-item > menupopup[placespopup="true"] menuseparator {
margin: 0 !important;
padding: 0 !important;
}
.subviewbutton.panel-subview-footer {
min-height: 1px !important;
border-top: none !important;
}
/* Pack more in vertically */

#BMB_bookmarksPopup menu, #
BMB_bookmarksPopup menuitem {
min-height: 1.5em !important;
}
/* Remove scrolling triangles from classic menu */
#bookmarksMenuPopup .autorepeatbutton-up, #bookmarksMenuPopup .arrowscrollbox-overflow-start-indicator,
#bookmarksMenuPopup .arrowscrollbox-overflow-end-indicator, #bookmarksMenuPopup .autorepeatbutton-down {
display: none !important;
}
/*收藏夹多列模式 end*/

大姥 win7 无边框失效了 能整不