pavucontrol vs firefox

i am running both pavucontrol and firefox in different workspaces (because firefox is playing a full screen video from youtube). the volume is way too low for that video so i switch workspace to where pavucontrol is showing. i click the "Output Devices" tab and set the speakers to 150% and then i click the "Playback" tab an set firefox to 150%. now the sound is high enough to hear so i switch back to the video. because i missed the beginning i back up the video by 10 seconds with key "j". it backs up but the audio goes lower when i do that. i return back to see pavucontrol and i find that firefox has lowered its volume. i repeat these settings but each time jumping back lowers the volume to 100% or lower. i want it to stay on 150% (which works and allows me to hear the audio) while i backup the video. any idea what's going on with firefox?

edit 1:

i tried this with both windows in the same workspace, but the same problem exists. if i move the position in time the volume setting is reset from 160% down to 100% and the audio goes down enough that i can't hear it any more. i wish i could set the speakers to 200% (anyone know how to do that?)