Druid Starfire glyph question

Druids have a major glyph that will extend the duration of the moonfire DOT by 3 seconds up to a maximum of 9 seconds. My question is how does this stack or synergy with multiple druids? For example, if I open with moon fire so the mob now has 4xDOT's. Then follow it up with 4x starfire (one casting), will that instantly push the dot out the 9 seconds or will it only extend that druids moon fire by 3 seconds. Also does the door swing both ways. 4xmoonfire, then have just one druid chain cast starfire to push out all the DOT's by 3 seconds a cast while the other druids spam wrath?

It only increases the duration of YOUR moonfire dot. So if you cast starfire 3 times in a row it will increase it by 9 secs total then any additional starfires wont have an effect. Other druid's starfires don't affect your moonfire dot.

Ok so a decent rotation with that glyph would be insect swarm, moonfire, 3x starfire, then spam wrath till the dot's expire.

Ill have to test but I think my starfire casting takes 2.3 seconds so not much of a time gain there to get more wraths off before refreshing, but 9 more seconds of a dot is going to be a nice increase in damage per mana as I already have the moonfire glyph that does 75% more dot.