Assuming this because of APZ changes. 1) Scroll the screen as slow as you can Expected: Screen scrolls Actual: Screen has a delta before it starts scrolling so the screen does not scroll, it triggers a long press, and a context menu appears. I do these minute scrolls out of habit while I'm reading, so it's causing me some UX issues where a context menu appears rather than scrolling the screen.
Bug 1231504 should have improved this somewhat, and bug 1230709 is on file for tweaking this further. See the comments on that bug for a pref change you can try locally for now.