STR: (Win7, Nightly 42.0a1 (2015-08-07)) 1. Open about:preferences#search 2. Edit keyword for any search engine by doubleclicking on it 3. Part of keywords may still be visible, especially for keywords starting with "/", "x" or "y" RESULT: I see some pixels from the selected blue row. I don't expect this. NOTE: You may not reproduce the 1st time. Try to reduce the window's width a bit, then try again. Don't confuse this behavior with bug 1192474. This reult is unstable but I can reproduce it in 50% cases. I'll be available until ~15 August (in case you'll need a screencast)