STR: (Win7_64, Nightly 43, 32bit, ID 20150907030206, new profile, safe mode) 1. Open Scratchpad (Shift+F4) 2. Type "document.body.on" 3. Press Ctrl+Spacebar [to open autocomplete suggestions] 4. Switch through them using Down arrow: press it until you switch to last suggestion, then press it 1 more time to switch to the 1st suggestion. Result: Suggestions twitching 1-2px up and down when you switch through them. Expectations: Suggestions should stay still I believe that the goal of that CSS file (chrome://browser/content/devtools/codemirror/codemirror.css) was to make them stand still. So I suggest the following changes to reach that goal Note that I had to change .CodeMirror-hints because codemirror scrolls suggestion into view leaving 3px on top/bottom of suggestion. I also had to add "margin-bottom:3px" for last sugestion if the list is scrollable due to bug 47710 > ul.CodeMirror-hints{ > padding: 3px; > /* hack due to CodeMirror scrolling */ > } > > li.CodeMirror-hint:nth-child(1n + 13):last-child{ > margin-bottom:3px; > /* hack due to bug 47710 */ > } I tested this with extension "Stylish" and it worked OK with both short and long lists. Please apply similar hack to CSS file currently used in Scratchpad (you may want to remove tags from selectors)

Scratchpad triage, filter on "ghostbusterzzz"