Steps how to reproduce with (Windows7 Basic Theme; WOW64; rv:29.0) Gecko/20100101 SeaMonkey/2.26 Build-Identifikator: 20140428215944: 1. Launch Browser, open Bookmarks in Sidebar (what should contain some folders) 2. Form an arbitrary Web Page (for example this bug report) Click Favicon in URL-bar and drag and drop it to Bookmarks in Sidebar. Beginning at the top for drag and drop move mousepointer down to find the location to where you want to drop the URL as bookmark AS expected: nearby mouse pointer always between 2 existing bookmarks a short thick line will be shown as plyce where the bookmark would be placed if you release mouse button Unexpected: When hovering folder names in the bookmark list, the folder name string will become invisible This problem is limited to Aero and WIN7 basic themes, does not appear with Classic Theme. High Contrast not yet tested

Also (High) Contrast No 1 not affected. I wonder whether this one might be related to "Bug 1023277 - Dropdown for mail view selector: "All" an "Unread" without text instead of highlighted with IWN7-Basic and Aero Themes" The string does not become really invisible, it stays in something between "dark white" and "light grey" with very small contrast to highlighted area. The problem also is visible with FF 30.0, but there the contrast is a little better, Folder name string keeps visible

You see the problem in screenshot showing Bookmarks Sidebar: highlighted folder name "Noch ansehen" color contrast to highlighted background is very small.

In all themes the folder name string color switches form black to white when the complete line gets the "selected" background bar. That is useful if the selected background bar has a dark color, but in Classic theme it's color is a very transparent and bright light blue with only very small contrast to the white folder name strings. Possible solution: folder name strings should stay in black during mouseover.

The same issue is presented on Firefox, so moving to toolkit -> Themes (instead of filing a new bug)

Proposed fix by overriding the dropOn color for Vista-Win10 with default themes.

Affected: Win7_64, Nightly 47, 32bit, ID 20160301030237 Fixed on: Win7_64, Nightly 47, 32bit, ID 20160306030215 Finally this is fixed after 3.5+ years.