I'm getting this message when I open Deezer on Firefox on Ubuntu 18.04.
Sorry, we don't support this version of your browser anymore. Update your browser or download our desktop app to keep enjoying your music.
If you are getting this above message
Sorry, we don't support this version of your browser anymore. Update your browser or download our desktop app to keep enjoying your music on Firefox for Deezer on Ubuntu 18.04 try this.
sudo dnf install https://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-$(rpm -E %fedora).noarch.rpm sudo dnf install ffmpeg
if this doesn't work or says that dnf not found then just try this
sudo apt install ffmpeg & close & reopen your firefox & hopefully it should work fine.
Now, the long story: I had to change my laptop a few times & every time it had a new copy of Ubuntu (18.04) installed so when I try to open Deezer on Firefox it would show this message. While I could use Deezer on Chrome just fine I couldn't get it to work on Firefox which I hated because I like using Firefox.
I managed to make it work on Firefox the first time I changed laptop but I forgot how I did that & when it happened again the second time I, of course, googled around & found the solution which I had to share. Turns out that Linux does not come out of the box with the correct encoder so there is nothing wrong with Firefox it's just Linux thing. I'm still not sure how it worked on Chrome though, I guess kudos to those guys.
here are a few links which helped me to resolve my issue.
for ffmpeg detailed installation instructions