Stop Sound Notification on Firefox Mobile Phone

Question

I use the HTML5 video tag as follows:

<video playsInline muted autoPlay className='video' preload='auto' loop='loop'> <source src="intro-m-no-audio.mp4" type='video/mp4' /> </video> 

As you can see, the muted attribute is set. In addition, I made sure that the video no longer has an audio track:

 avconv -i intro-m.mp4 -vcodec copy -an intro-m-no-audio.mp4 

this gives:

 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'intro-m-no-audio.mp4': Metadata: major_brand : isom minor_version : 512 compatible_brands: isomiso2avc1mp41 creation_time : 2017-04-13 15:01:27 encoder : Lavf53.21.1 Duration: 00:00:08.40, start: 0.000000, bitrate: 2104 kb/s Stream #0.0(und): Video: h264 (Baseline), yuv420p, 960x540 [PAR 1:1 DAR 16:9], 2102 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc Metadata: creation_time : 2017-04-13 15:01:27 

As you can see, there is no more audio stream.

YET, every time I open a page on Android Mobile Firefox (v53), my Spotify player stops playing and an annoying notification video appears. This does not happen in Chrome (on Android). How can I prevent this?

EDIT . Here's a live example to understand what I mean: https://www.srf.ch/static/srf-data/data/2017/pendler/#/de