Works as expected, adds a progress and volume slider underneath the videos, including reels, it's baffling that in this day and age Facebook expects you to lower you whole system or whole browser volume to not get your eardrums ruptured when watching a video, or that you need to rewatch it from the beginning to see an specific part of the video, oh well, that's enshitfication for you.
My only gripe with this addon is that when you reload the page the volume slider goes back to 0, but I think this is an limitation either of Firefox or Instagram's site.