Try to remove the other prefs that show in the screenshot (especially the app pref) and only leave the expose pref with value false. You can also check the handlers.json file in the profile folder.
[ Source: npapi-vlc ]
Links for browser-plugin-vlc
Debian Resources:
Download Source Package npapi-vlc:
Maintainers:
Debian Multimedia Maintainers (QA Page, Mail Archive)
Benjamin Drung (QA Page)
Reinhard Tartler (QA Page)
External Resources:
Homepage [www.videolan.org]
Similar packages:
multimedia plugin for web browsers based on VLC
This plugin adds support for MPEG, MPEG2, DVD, DivX, Ogg/Vorbis and manymore formats to any Gecko-based web browser (Firefox, Galeon, etc.). Thedecoding process is done by VLC and the output window is embedded in awebpage or directly in the browser window. There is also support forfullscreen display and javascript control.
VLC is the VideoLAN project's media player. It plays MPEG, MPEG-2, MPEG-4,DivX, MOV, WMV, QuickTime, WebM, FLAC, MP3, Ogg/Vorbis files, DVDs, VCDs,podcasts, and multimedia streams from various network sources.
Other Packages Related to browser-plugin-vlc
depends
recommends
suggests
enhances
dep:libatk1.0-0 (>= 1.12.4)
ATK accessibility toolkit
dep:libc6 (>= 2.14) [amd64]
GNU C Library: Shared libraries also a virtual package provided by libc6-udeb