Migrating native Firefox to Flatpak in XFCE
This is what I did...
Initially visited the Flatpak setup page and then followed up the instructions there with
flatpak update and
flatpak install flathub org.mozilla.firefox
I followed the instructions here.
about:profiles to find out which profile my current Firefox used.
Then I used this command
flatpak override --user --filesystem=~/.mozilla org.mozilla.firefox to allow Flatpak-Firefox to access the profiles.
Closed Firefox-ESR and opened Flatpak-Firefox,
about:profiles again, find which profile was being used before and set that as default and open it in a new window.
Setting as Default
I followed these instructions
xdg-settings set default-web-browser org.mozilla.firefox.desktop
xdg-settings check default-web-browser org.mozilla.firefox.desktop
to ensure it was set properly.
I had to run this command
flatpak install ffmpeg-full and then selected option 3 which was for the 21.08 version.
Videos now work!
I hope this is handy for someone out there. It worked flawlessly for me; no signing back in to sites and kept all my customisations/personalisations too.