media keys cannot control any websites on linux

i've tried toggling ''media.hardwaremediakeys'' off and pressing the media keys to no avail, they don't seem to have any effect when it's enabled or disabled. the keys work on other applications like VLC media player, though! and I can see that the media is being detected from firefox, too, as it appears in media player widgets i have on my plasma desktop. it seems to be ''only'' the physical keys that aren't working, because i can press buttons on the widgets to control media playing in firefox.