The source-list and variables view in the debugger no longer respond to the scroll wheel for me. However, the editor view does. I'm using today's fx-team on linux. It's simplest to see with a mochitest. Run ./mach test test_saveHeapSnapshot_e10s_01.html After it is done, open the debugger. I try to scroll the list of sources with the scroll wheel, but nothing happens. Then, set a breakpoint somewhere in the test and reload. When the debugger stops, expand enough variables so that the variables view can be scrolled. Now try the scroll wheel there -- for me it does nothing. Moving the mouse over the scrollbar does not help, in case this matters.