Scrolling with mousewheel or middle and left clicks actions are not working on the left most edge in KDE Plasma 5.10.5, when window is maximized. I.e. Firefox doesn't react, it's as if something is swallowing those actions. Not sure whether it's Firefox or Plasma related. I filed Mozilla bug here as well: https://bugzilla.mozilla.org/show_bug.cgi?id=1396445 Configuration: Debian testing x86_64 KDE Plasma: 5.10.5 Firefox 56.0b9 Qt5: 5.9.1 GTK3: 3.22.19
Believe it or not, somebody else has already reported the same problem, and it looks like a KWin issue. You can close the upstream Mozilla bug report. If you can use the Plasma Wayland session, it's not a problem there. Folks are still looking for a workaround on X11. *** This bug has been marked as a duplicate of bug 384269 ***