Description of problem:
After clicking a system notification or opening the "hidden icons", the mouse wheel no longer works in Firefox.

Version-Release number of selected component (if applicable):
plasma-desktop-5.3.1-3
firefox-38.0.5-1

How reproducible:
Always

Steps to Reproduce:
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.

Actual results:
No scrolling

Expected results:
Other windows eg dolphin do not stop scrolling

Additional info: