Where are you seeing that? I don't see it anywhere. It may be caused by your userchrome file. Is the problem still there if you start Firefox in troubleshoot mode?

https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode

Hello,

It was not the css customization. Not sure what it was but I managed to "fix" it playing a bit, both in the tree and items.

-moz-any(#bookmarks-view, #historyTree, #editBMPanel_folderTree, #placesList, #placeContent)

treechildren::-moz-tree-row(selected, focus) {

 margin-top: 0px !important;
 min-height: 14px !important;
 height: 21px !important;
 outline-style: none !important;

}

It would look better with less height but I'm happy with the result. Attached screenshot.

Just as a side note. Yesterday I had the post ready with another issue already fixed and forgot to edit the subject. Would be great if you or any admin could edit it with a better description.

Edit: Updated the post title. I didn't know I could do it myself.

Thanks for your time.

Regards.

Solved it! Now matchs perfectly with my desktop theme.

This is the code just in case someone needs it.

treechildren::-moz-tree-row {
  margin-top: 1px !important;
  min-height: 14px !important;
  height: 18px !important;
  outline-style: none !important;
}

Regards.