So posting here since I know reworks for fire shield are planned.
Something I’ve recently discovered that I like with this skill is when you’ve speced in the “can cast on Allies” node. This opens up the possibility of casting it on your minions (mirror mage). The CD is only one second, so you can cast it on a very large number of minions, at a decently high Mana cost. It no longer feels passive as you’re casting it frequently and making decisions on which character to cast it on, while also managing Mana.