Customer observed unwanted highlighting of the content in UDW.

Steps to reproduce:
1. Enter Content->Content Struture->Content browse menu
2. Select one content and move cursor over another.
3. See that all the text which lies under the moving cursor is highlighted.

The observed behavior is presented on the attached video. The only browser which is affected is Firefox (tested on 60.0.1, the customer uses 60.0.2).