Опять столкнулись с кривым переводом.

Оригинальное описаниe (http://www.wowwiki.com/Glyph_of_Fire...?oldid=2406309)

Increases the critical strike chance of Fire Blast by 50% when the target is stunned or incapacitated

Ни о каких обездвиживаниях (root) ничего не сказано.

Ищем дальше:

http://www.wowwiki.com/Incapacitate
Incapacitate or Knockout, previously called Disorient, is a form of crowd control that render a player or NPC unable to move or act for a short period of time. Incapacitate differs from Stun in that Incapacitate effects always break on damage, while Stun effects don't. Incapacitate effects are also often harder to break free from; a mage can for example break a stun by using Blink, but will be unable to do so if incapacitated.

Example of Incapacitate effects:

Rogue: Gouge
Paladin: Repentance (Talent)
Druid: Maim
Engineering gizmo Goblin Rocket Helmet and most bombs and grenades.
Horned Viking Helmet, a drop from Eric "The Swift", an elite dwarf only killable by Horde characters in Uldaman.

Т.о. перевод - кривой. Символ работает корректно