How do I install and migrate to the official Firefox flatpak?

I would like to install Firefox via Flathub while ensuring that I am using an official build from Mozilla and not a repackage/PPA.

Backing up your existing profile

Before we begin we should always back up our stuff, even if you're using Firefox Sync

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Install Flathub

Mozilla publishes Firefox directly into Flathub, however we need to turn this on in Ubuntu. Follow these instructions, I am summarizing them below:

sudo apt install flatpak
sudo apt install gnome-software-plugin-flatpak
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo    

Install Firefox

This will install Firefox and the corresponding ffmpeg libraries so videos, etc work:

flatpak install flathub org.mozilla.firefox org.freedesktop.Platform.ffmpeg-full/x86_64/20.08

Then the Firefox icon will appear in your menu/overlay, or you can do flatpak run org.mozilla.firefox to launch it from the command line.

Migrating your profile

[todo]

Reusing your old profile

You can also reuse your profile without manually copying it over though this probably isn't a good permanent solution.

Quit firefox, then do

flatpak override --user --filesystem=~/.mozilla org.mozilla.firefox

to have the flatpaked Firefox reuse your old profile.

Checking your work

Clicking on the burger menu -> Help -> About Firefox will show "Mozilla Firefox Flatpak" and "mozilla-flatpak" in the dialog window:

Okay, so I just did this successfully (on Arch / EndeavourOS). So I'm putting it down here, in case anyone wants to know how.

On Linux your Firefox profiles are typically stored at:

~/.mozilla/firefox

There might be multiple profiles in there. Profiles are directories, with random names, but usually followed with something like .default-release or .default. You can find out which your profile is by running Firefox with -P (so just firefox -P on the terminal). That's the profile you want to save (you could move all the profiles over as well).

(Optional Step: even though it's not actually necessary, I would back up your profile data. If you have a folder ~/backups, I'd run rsync -a ~/.mozilla/firefox ~/backups/ to copy it over.)

First, I'd install the native non-Flatpak system Firefox. On Arch, this is done with sudo pacman -R firefox, and on Ubuntu, it's probably sudo apt remove firefox.

Second, install Firefox from Flathub. Run flatpak install org.mozilla.Firefox. Don't launch the newly installed Firefox yet.

Note: the Flathub Firefox's firefox folder lives here:

~/.var/app/org.mozilla.firefox/.mozilla/firefox/

Now, move your old profile(s) into this folder. What I did was:

1. Move my specific profile folder. So: mv ~/.mozilla/firefox/abcd123e.default-release ~/.var/app/org.mozilla.firefox/.mozilla/firefox/ (where abcd123e.default-release is your profile folder now)

2. Copy profiles.ini file over similarly (if one doesn't already exist for the Flathub Firefox -- it shouldn't, if you didn't open it). After copying it, delete the [InstallXXX....] section.

(You could just overwrite the whole firefox folder I suppose, but I haven't tried that.)

That's it. I launched the Flathub Firefox, and everything was working perfectly fine, and as expected.