fedora 22 mouse wheel in KDE [closed]

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I can confirm your observation, having just tried it out, myself. With Firefox already open on a scrollable web page, I followed this procedure:

1) Open Firefox, navigate to a scrollable web page and confirm that the mouse wheel works as expected with the web page.
2) Click the upwards chevron in the KDE system tray to produce the "Status and Notifications" window.
3) Click the downwards chevron to hide the window.
4) Click on the web page in Firefox to regain focus for the Firefox application.
5) Confirm that mouse wheel scrolling no longer works.
6) Click on any other open application to give it focus.
7) Click back on the web page in Firefox to regain focus for the Firefox application.
8) Confirm that mouse wheel scrolling works again as expected.

Good find; you can submit a bug report at https://bugs.kde.org/ .