I have a question regarding the priorities as they stand right now. Currently, if you get an FoF proc with no BF proc, you will cast Ice Lance. FFB is reserved for instances in which you have both FoF and BF up. It seems to me that, factoring in Ignite and the new FFB glyph, that there should be a point at which a slowcast FFB will do more than throwing an IL and part of a FB.
The main reason a "slowcast" FFB is not superior to Ice Lance on a Fingers of Frost proc is because Fingers of Frost does not affect a regular-cast FFB. Fingers of Frost only affects the Brain Freeze'd, instant FFB, and it says so on the tooltip.Brain Freeze - Spell - World of Warcraft
Second sentence from the last, "When Frostfire Bolt is instant, it can benefit from Fingers of Frost."
So without the Fingers of Frost benefit (and it won't even eat up a charge of FoF either), a regular FFB will do... the regular amount of damage, so there's a lot more ground it has to cover before it can outdamage the instant Ice Lance. If it ever could. That's something I'll have to do some figuring on.
What I am unable to factor is the chance of procs. Now, currently, FFB is still generating FoF and BF procs, even though the chill effect is removed by the Glyph. I do not know whether this is intended, or a bug. If it is intended, then there are no missed proc chances to factor in.
What Tyrian suggested about the "non-slowing chill effect" sounds right on.
Consider what the Glyph of Frostfire says: "but no longer reduces the victim's movement speed." It definitely doesn't say it doesn't chill anymore, and generally (or at least I'm viewing the past with rose-tinted glasses) Blizzard picks their tooltip words carefully.
Frostfire Bolt certainly does proc FoF, but I've never seen it proc Brain Freeze. If it did, that
would be unintended, as the Brain Freeze talent says that FFB can't proc it.
Here, I poked a target dummy for 5 minutes with FFB only. FoF procs galore, but 0 BF. One could argue RNG, but it doesn't seem likely to me.12/5 16:34:48.179 SPELL_CAST_START,0x0600000003B2 - Frostfire Bolt testing
Edit: Well, I took far too long in typing this up. Someone already beat me to the punch.