Unless you installed the developer edition, which uses a separate profile/path, both of your installs will use the ~/.mozilla directory, so configs and profile of your new install will interfere with the ESR version.
(and why did you symlink /opt/firefox/firefox to /usr/bin/firefox? The desktop file already takes care of recognition)
This won’t work as expected, I don’t think?
Unless you installed the developer edition, which uses a separate profile/path, both of your installs will use the ~/.mozilla directory, so configs and profile of your new install will interfere with the ESR version.
(and why did you symlink /opt/firefox/firefox to /usr/bin/firefox? The desktop file already takes care of recognition)