In a recent hotfix, Spellfire Spheres for Arcane and Fire Mages now regenerate quicker out of combat! Arcane Mage DPS GuideFire Mage DPS Guide The Sunfury hero talents for Arcane and Fire Mages include Spellfire Spheres, stacking up to 5 with the talent Rondurmancy.
These spheres increase damage by 2% for Arcane and 1% for Fire per sphere, leading to a large spell damage buff when you have all of them active.
When out of combat, these used to very very slowly regenerate, and only to a maximum of 3. However, especially when you're going for maximum DPS like in the Race to World First, you would want to start with all 5 orbs and this was possible, just very time consuming.
After every pull, a Mage could theoretically portal back to town and hit a training dummy to generate max stacks before the next pull.
Thankfully, this is no longer needed as Spellfire Spheres now regenerate much quicker and to the maximum stacks of 5 now as well.