In the sidebar and in the Bookmarks Manager (Library) you have treechildren type of content and this doesn't allow to affect/hide specific content via userChrome.css. This is only possible in a menu type list like the toolbar Bookmarks Menu button and in the Bookmarks menu. You can't remove any of the root folders that appear directly under the "All Bookmarks" folder. Note that in some case you only see the Other Bookmarks folder when there are bookmarks stored in this folder, same for mobile bookmarks from other devices.

Sorry to hear that :(

I have another question that bothers me. It's about reducing the right drop-down menu. I outlined my issue in uploaded short video of my Mega cloud - https://mega.nz/file/kuYDBAYD#rXUJNbw0YJqEWJLpIUijz9kQ12tCZFd6CiTPWT3MWbc

I'd like to tighten them up the same way like I did for left bookmarks toolbar due to userChrome.css: (and set the space to 2x, just excellent!) ______________________________ /*** Tighten up drop-down/context/popup menu spacing (8 Sep 2021) ***/

menupopup:not(.in-menulist) > menuitem, menupopup:not(.in-menulist) > menu {

 padding-block: 2px !important; /* reduce to 3px, 2px, 1px or 0px as needed */ 
 min-height: unset !important; /* v92.0 - for padding below 4px */

}

root {

 --arrowpanel-menuitem-padding: 4px 8px !important;

} _____________________________

Could you help me finding solution for this at least?? I'd really appreciate your help.

I use CSS code like this in userChrome.css that works in Compact mode.

• https://support.mozilla.org/en-US/kb/compact-mode-workaround-firefox
• about:config => browser.compactmode.show => true

:root[uidensity=compact] menupopup :is(menu,menuitem) {
 padding-block: 2px !important; /*adjust: 0px-4px*/
 min-height: 22px !important;   /*adjust: 21px-24px or unset*/
 height: 26px !important;       /*adjust*/
}
:root[uidensity=compact] {
 --arrowpanel-menuitem-margin: 0 4px !important;
 --arrowpanel-menuitem-padding: 2px 6px !important; /*adjust 2px value*/
}

For the sidebar and the Library (treechildren), you can use this CSS code.

:is(#bookmarks-view, #historyTree, #editBMPanel_folderTree, #placesList, #placeContent)
treechildren::-moz-tree-row {margin-top: 0px !important; min-height: 22px !important; height: 22px !important;}

Unfortunately, It did not help at all.

Note that the code only works if you have enabled "Density: Compact mode" in the Customize page (or leave out [uidensity=compact]). The sidebar code doesn't has this restriction.

Does other CSS code in userChrome.css work? You can try a userChrome.css with only the code I posted above as a test in case there is a problem with your current userChrome.css.

Note that the code only works if you have enabled "Density: Compact mode" in the Customize page (or leave out [uidensity=compact]).

I know that. I was trying separately to put these css one by one, but it's not effected the reducing right drop-down menu.