Sometimes I can see flickering of menus in different programs. I see it in
firefox but also plasma menus running TW snapshot 20160523 after some updates
of xcb-packages.

In xsession.errors I can see this:
QXcbConnection: XCB error: 2 (BadValue), sequence: 48562, resource id:
18874508, major code: 142 (Unknown), minor code: 3
QXcbConnection: XCB error: 2 (BadValue), sequence: 48566, resource id:
117440516, major code: 142 (Unknown), minor code: 3
QXcbConnection: XCB error: 2 (BadValue), sequence: 48653, resource id:
18874508, major code: 142 (Unknown), minor code: 3
kdeinit5: Got EXT_EXEC '/usr/bin/dolphin' from launcher.
kdeinit5: preparing to launch '/usr/bin/dolphin'
QXcbConnection: XCB error: 3 (BadWindow), sequence: 27051, resource id:
125829120, major code: 18 (ChangeProperty), minor code: 0
no winId: probably startup task
QXcbConnection: XCB error: 3 (BadWindow), sequence: 27055, resource id:
125829121, major code: 18 (ChangeProperty), minor code: 0
Cannot creat accessible child interface for object:  PlacesView(0x2193b10) 
index:  18
no winId: probably startup task