Per Mozilla's PR here [https://phabricator.services.mozilla.com/D156233], session and dynamic rulesets are applied at a higher priority than the static rulesets defined in the manifest.

• When multiple rules match, the order between rules are defined as follows:
• • Ruleset precedence: session > dynamic > static (order from manifest.json).
• • Rules in ruleset precedence: ordered by rule.id, lowest (numeric) ID first.
• • Across all rules+rulesets: highest rule.priority (default 1) first, action precedence if rule priority are the same.

Safari does not give session and dynamic rulesets higher priority when determining which rule to apply.