I fixed it by installing the package generated by the pipeline of the pending merge request of v4 of firefox-esr-mobile-config (Document and release 4.2.0-1pureos1~byz (!6) · Merge requests · Librem5 / debs / firefox-esr-mobile-config · GitLab)
wget https://source.puri.sm/Librem5/debs/firefox-esr-mobile-config/-/jobs/429326/artifacts/raw/debian/output/firefox-esr-mobile-config_4.2.0-1pureos1~byz+librem5ci86029.b7a9841_all.deb
sudo apt install ./firefox-esr-mobile-config_4.2.0-1pureos1~byz+librem5ci86029.b7a9841_all.deb