Although this is not Qubes OS specific, it seems a lot of people struggle installing Librewolf on their qubes, so here is a short community guide explaining how to proceed.
ℹ️ Tested on Debian 12 xfce
From https://librewolf.net/installation/debian/
sudo apt update && sudo apt install extrepo -y
sudo env https_proxy=http://localhost:8082 extrepo enable librewolf
sudo apt update && sudo apt install librewolf -y
ℹ️ Tested on Fedora 42 gnome (the template called fedora-42)
From https://librewolf.net/installation/fedora/
curl -x http://localhost:8082 -fsSL https://repo.librewolf.net/librewolf.repo | sudo tee /etc/yum.repos.d/librewolf.repo
sudo dnf install librewolf
You will be prompted about this
Importing OpenPGP key 0x2B12EF16:
UserID : "LibreWolf Maintainers <gpg@librewolf.net>"
Fingerprint: 662E3CDD6FE329002D0CA5BB40339DD82B12EF16
From : https://repo.librewolf.net/pubkey.gpg
Is this ok [y/N]:
Make sure the fingerprint matches the one found in librewolf website (linked just above), press "y" and "enter". Then you will be prompted if you accept to install librewolf, press "y" and "enter".