1. Enable three-finger swipes on OS X http://apple.stackexchange.com/a/73503/2246 2. Run nightly using a clean profile 3. Open a page that is long enough to scroll vertically, e.g. https://wiki.mozilla.org/Electrolysis 4. Swipe down with three fingers Actual results: the page scrolls to the bottom 5. Use File -> New e10s Window 6. Open the same long page as in #3 7. Swipe down with three fingers Actual results: the page does not scroll at all. Two-finger scrolling still works. Tested on 2014-09-12 nightly (also tested a nightly from 2014-08-16 with the same result), OS X 10.9.4, Macbook pro.
To elaborate on step 1: the setting is System Preferences -> Trackpad -> More gestures -> Swipe between pages -> set to "Swipe with three fingers".