I only partly understood what I was reporting in bug 355102: now the funkiness with the splitter cursor sticking around is gone, but either the Firefox sidebar *or* the content window reacts to hovering, where on other platforms and with Widget: Mac both do. STR: 1. Load https://bugzilla.mozilla.org/show_bug.cgi?id=355102 and make sure the attachment table is visible. 2. Open the History sidebar, expand the tree until you see the entry for that page. 3. Hover the entry in the sidebar: you should see a tooltip with the full page title. 4. Hover the link for "Fix v1.1" in the attachment table in the content window: you should see a tooltip saying "View the content of the attachment" but you won't. 5. Click the background of the content window, then hover the "Fix v1.1" link again: now you will see the tooltip. 6. Hover the item in the sidebar again: now you won't see a tooltip there.

Fixed by the patch on bug 376811.