First suggestion is to use GPO ( https://github.com/mozilla/policy-templates/releases ) or Enterprise Policy Generator add-on by Sören Hentzschel for manage security settings (so Mozz can't override user preferences), the second is to use ESR releases to avoid this kind of issues.
Try disable/re-enable the preference "Add the root certificate to known browsers" under "web and mail"-"ssl-tls" and check if Eset cert has been added to the browser. (just tested with ESR and it works)
Check also for "security.certerrors.mitm.auto_enable_enterprise_roots" (true) https://support.mozilla.org/en-US/kb/how-disable-enterprise-roots-preference
