Rule comparison feature helps to compare the rule sets between two configuration files or between two running config versions and helps to identify the rules that are added, deleted, modified. It also helps to identify which rule field is modified in that particular rule.
Yes, you can compare between change config versions by choosing the option 'Between Running Config Versions'. Choose any two config versions and compare the rule sets.
Rule comparison report will show the comparison result only if there is any changes available between the firewall rule sets. The other configuration changes that are not related to firewall rules are not taken into account. If same set of rule sets exists in both the files, Firewall Analyzer results in 'Both the files selected for viewing diff are the same'.