Style to remove history icons from "library" window

[delicacy]

I removed the cache of websites for icons, & i'd like to hide those blank icons from the history (only - not bookmarks) section of the library window..
but i don't have the whole code's location..

but only & probably the end of it:
treechildren::-moz-tree-image { width: 0 !important; }



anyone has a location code to hide those blank icons ?

[delicacy]

anyone ?