Comment 7 for bug 1720908

Thanks Tom, i tried but as per googling i found we cant revert back automatically to older version. Only solution is to uninstall the current version and manually install old version from source.

sudo apt-get install firefox=55.0.2+build1-0ubuntu0.16.04.1
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Version '55.0.2+build1-0ubuntu0.16.04.1' for 'firefox' was not found