Since Ubuntu 22.04, firefox is based on snap, with various side effects, including inability to download files in fuse.fs mounted partitions. This post explains how to install firefox from mozilla repository instead.

Special thanks to Stéphanie who had a problem with her mounted partitions and pointed the issue to me so that I could fix it for her!

Important warning! Before you start, be sure to have saved your user profile (it is especially important if firefox stores for you your passwords or other login information). This can be done:

• either by activating your firefox sync account. In this case, activating the same sync account on any brand new firefox will automatically activate your formally saved passwords and downloaded plugins;
• or directly save the snap user profile (included in ~/snap/firefox/common/.mozilla/firefox). After firefox has been reinstalled, it can be copied into ~/.mozilla/firefox/.

Special thanks to >Pierre who had to experience the loss of his data and pointed that issue to me.

Finally, to install the mozilla repository based version of firefox, first remove firefox based on snap:

sudo snap remove firefox

and add mozilla PPA in you source list:

sudo add-apt-repository ppa:mozillateam/ppa

Then, as sudo, create a file /etc/apt/preferences.d/mozilla-firefox where you put the following lines:

Package: *
Pin: release o=LP-PPA-mozillateam
Pin-Priority: 1001

Package: firefox*
Pin: release o=Ubuntu
Pin-Priority: -1

To finish,

sudo apt update
sudo apt upgrade
sudo apt install firefox

should be enough to properly install firefox (and as an extra surprise, install a better version of thunderbird, compatible with more plugins, including the TbSync plugin that is the only one to handle Active Directory synchronization and is not functional in Ubuntu official release of thunderbird).