SUMMARY When using Firefox in Plasma/Kwin (X11 and Wayland) scrolling on a page is unpredictable. Scrolling down a few turns of the mouse wheel and stopping makes the page bounce back up to the top and then start scrolling, without mouse input, back down slowly. STEPS TO REPRODUCE 1. Open Firefox 2. Navigate to a web page with scroll bars (e.g., a Wikipedia entry) 3. Scroll down with the mouse wheel OBSERVED RESULT EXPECTED RESULT SOFTWARE/OS VERSIONS Linux/KDE Plasma: Arch 5.14.6-arch1-1 64 bit (available in About System) KDE Plasma Version: 5.22.5 KDE Frameworks Version: 5.86.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION NVIDIA graphics card May be related to https://bugs.kde.org/show_bug.cgi?id=387797 or https://bugs.kde.org/show_bug.cgi?id=438326 See Bugzilla report here: https://bugzilla.mozilla.org/show_bug.cgi?id=1727091
If it happens on X11 too, then KWin can't be involved, because KWin only processes input events on Wayland. That means it must either be a bug in Libinput (the input driver) or Firefox itself (in how it receives those events). It's definitely not related to Bug 387797 that only affects Plasma applets using the PlasmaExtras.ScrollArea component. And if it was Bug 438326, then the issue wouldn't happen on X11.