This happens with youtube in firefox. If I run it fullscreen on my side monitor and then click anywhere on my other monitors, the taskbar shows up above it. Same thing happens with VLC. The taskbar also shows up the moment I click on the control window of VLC. Running firefox itself fullscreen with F11 also experiences the same issue.
I included the log file.
Edit : Never mind, saw it in settings, I don't know how it got activated.