I have just opened your master version of Phabricator and noticed that the right edge scroll bar is broken in multiple ways. It seems you have disabled browser-native scroll bar and use some javascript stuff instead.
This is what is broken:
1. If I have browser maximized and move my mouse cursor to the very right (the very last pixel on the screen) and try to grab the scrollbar, it performs a "page down" instead. So not only I cannot grab the scrollbar, it slides down. If I want to grab it, I must not be at the very far right, I need to move a few pixels away from the screen edge. Then I can grab it.
2. There's no mouse over effect nor drag active effect of the scroll bar, so it's very hard to find out when I can drag the scrollbar and whether I was successful in getting hold of it or not. That results in many failed attempts, and it keeps me on my toes. I can no longer just scroll the page without thinking.
3. Left click anywhere in the scroll trough should move the bar exactly to the same spot where the cursor is, effectively performing "jump to this position" move. Instead, I see a regular "page up" or "page down".
4. Right click anywhere in the scroll trough should perform fluent "page up" or "page down". Instead, it performs an instant move (no animated move, not fluent) and it displays a context menu as well, which I need to cancel.
Expected behavior in 2), 3) and 4) might be OS specific, I have no idea how it works elsewhere. But this behavior is consistent between apps and also between web pages in my system. It works the same everywhere, except for Phabricator site.
I don't know what is the reasoning and the intentions behind the scrollbar change, but please, consider this again. If you break the OS-native behavior of scrollbars, many users will be very unhappy. Scrolling is something you really want to have consistent system-wide, and not application-specific.
Thanks.
Firefox 35, GNOME 3.14, Fedora 21
your version of Phabricator, I don't know how to find out which one that is, doesn't seem visible anywhere