Great mod so far. A few comments:
--Rather than unwittingly extending combat log range for people, it's probably better to just use SendAddonMessage to sync up Combustion usages (same with detection of other people's crits once the stack is already at 5).
--Can you modify the graphic to make the number of Ignites a touch more visible? The 5 bars you have there now are a nice idea, but very, very tiny.

Forgive me for bumping this thread, but something's been bugging me lately about ignites, and I thought the posters here could provide some insight.

I recently respecced to fire (12/36/3) after being frost specced for over a year. When using Combustion, it is not unusual to get 3 Fireball crits in a row. I've been observing the ignite stack when this happens, and I've noticed the following: first Fireball crits, ignite goes up on the target and ticks once; second Fireball crits, ignite stack goes up to 2; third Fireball crits, but the old ignite stack is gone, and a new one is started. How is this possible?

My only explanation is that ignite is simply getting bumped off due to the debuff limit, but I'm still suspicious, as this has happened several times now. Anyone have similar experiences?

Well, assuming you have 5/5 imp. fireball, your spells would still land three seconds inbetween. That is, when your third fireball crits, the ignite timer will just have ticked out when the spell lands.

I feel stupid now. For some reason I was thinking the ignite would last 4 seconds after the second crit, which is obviously not the case. Thanks. :)

Correct, it's nice for early Thaddius, for 1 mage to pop fetish and grab credit for the ignite stack just before everyone else blows combustion.