How does Death Fire Touch work when hitting enemies with multiple skills?

Here is the wikia page on Death Fire Touch

• Deathfire Touch is a spell effect and will only be applied to instances of ability damage.
• The damage from this mastery does not trigger itself nor other spell effects.
• Multiple instances of damage will refresh the duration but does not stack. & On DoTs the duration of the effect is: DoT's duration + 1 seconds.