Bubble Hearth
The content of this article is not part of official Warcraft lore, but has nevertheless become part of the World of Warcraft culture or community.
Bubble Hearth (aka bubble-hearth) is a Paladin trick used to teleport away from nearly any threat in the game. It is performed by casting 
[Hearthstone] while protected by 
[Divine Shield], preventing enemies from interrupting the Hearthstone cast.
Although very useful, bubble-hearthing is generally viewed as a cowardly act and those who use it are often mocked for doing so. Of course, this tactic has to be used when necessary, such as when a roaming paladin finds himself unfairly situated against multiple foes and does not stand any chance of emerging victorious. In such situations, the Bubble Hearth is more of a smart move than a cowardly one. Indeed, wise (and fearless) paladins may realise that the most challenging and courageous path of all is at times to remove themselves from battle, and bubble-hearthing paladins can hold their heads high in the knowledge that they are making a most Righteous Retreat.
Bubble-hearthing paladins are largely immune to enemy attacks thanks to [Divine Shield]'s effects. However, Priests' 
[Mass Dispel] spell and Warriors' 
[Shattering Throw] are capable of removing this immunity. Paladins can reduce the likelihood of this happening by pre-emptively using CC abilities such as 
[Hammer of Justice] (
[Fist of Justice]) or 
[Repentance] on enemies capable of removing Divine Shield. The duration of these abilities will potentially keep the target out of action long enough to prevent them from interrupting the paladin's Hearthstone cast.
Debate
Bubble Hearthing has long incurred the wrath of non-paladins. Seen as a cowardly move, it allows paladins to escape defeat (or simply avoid PvP entirely), in a manner that may be considered unfair by their opponents. Bubble Hearthing and its debatable fairness has been the subject of much discourse within the community, including the creation of numerous videos and even a song (see below).
As a method of avoiding an otherwise inevitable defeat, Bubble Hearthing can be frustrating for the paladin's attackers, as it may deprive them of the glory and satisfaction of finishing their opponent. However, it should be remembered that many other classes have similar capabilities, and when faced with a no-win situation will also often choose to flee combat rather than stand and fight (and die). A prime example of this behaviour would be rogues, with numerous abilities such as 
[Vanish] and 
[Sprint] designed to allow for a swift exit should things turn sour.
While still generally considered a cowardly move, Blizzard's explicit re-implementation of Bubble Hearthing with 
[Glyph of the Righteous Retreat] can be seen as at last ending the debate regarding its overall validity. While the decency of Bubble Hearthing may continue to be disputed, it is at least clear that the trick is (now) intended to be part of the paladin's repertoire. The glyph's tongue-in-cheek title, as well as in-game references such as those listed below, also reveal Blizzard's awareness of the community's attitude toward the trick.
Official references
It is unknown if Blizzard planned the Bubble Hearth to be a paladin tactic, although it's likely that its existence was merely a coincidence. Even so, Blizzard seems to have since embraced the Bubble Hearth as an iconic feature of the paladin class.
- If the player equips an
[Argent War Horn] and uses it, a paladin from the Argent Dawn will appear, fight for 30 seconds, and then despawn by the humorous method of Bubble Hearthing. - A fortune by Sayge tells: "Divine Shields and Hearthstones do not make a hero heroic."
- [Glyph of the Righteous Retreat] explicitly confers the ability to Bubble Hearth (see below).
- Several paladin characters in the Legion expansion, such as Orik Trueheart during the
[Truthguard] acquisition scenario, use bubblehearthing to move around. - The April Fools' Day patch 8.8.8.88888 notes alluded to Bubble Hearthing: "
[Divine Steed] updated to look less like you’re just running away from a fight, except when followed by the use of Divine Shield and Hearthstone." - In Heroes of the Storm, one of Yrel's talents is Bubble Hearth, which allows her to become invulnerable and teleport to the Hall of Storms.
Other
There is even a song made by players relating to this act:
- "I'm a little paladin, short and stout.
- Here's my hammer and here's my trusty mount.
- When I get in trouble I scream and shout,
- then I bubble and hearthstone out!"
History
Pre-Cataclysm
Before Patch 4.0.1, the Bubble Hearth was performed simply by casting [Divine Shield] followed immediately by [Hearthstone]. This worked because the duration of Divine Shield (then 12 seconds) overlapped the Hearthstone's cast time (10 seconds).
Cataclysm
With Patch 4.0.1, the duration of Divine Shield was reduced to 8 seconds, whereas the casting time of Hearthstone remained at its previous duration of 10 seconds, making the Bubble Hearth impossible.
However, there still remained ways of replicating the tactic: when wearing 4 pieces of the Tier 7 Protection Set (level 80), the set bonus increased the duration of Divine Shield (and Divine Protection) by 3 seconds, allowing you to negate the nerf and still make a glorious exit.
Another solution was (and remains) 
[The Last Relic of Argus], an item from archaeology. Having a cast time of 5 seconds, it can effectively replace the Hearthstone as a teleportation item. The only downside is that it has a 12 hour cooldown, and teleports the user to an unpredictable and usually rather undesirable location.
These options aside, the Bubble Hearth remained impossible throughout Cataclysm.
Mists of Pandaria
Bubble Hearthing officially returned to the game in patch Patch 5.0.4 with the introduction of [Glyph of the Righteous Retreat], a minor glyph which reduces Hearthstone's cast time to 5 seconds when under the effect of [Divine Shield]. Since Divine Shield lasts for 8 seconds, this gives the paladin a 3-second window in which to cast the Hearthstone (as opposed to the 2-second window possible before Patch 4.0.1).
Legion
Patch 7.0.3 removed Glyph of the Righteous Retreat while making its effect baseline for all paladins.
Classic Hardcore
In continuance of the unofficial fan-made ruleset for World of Warcraft: Classic Hardcore, Paladins are unable to use their Hearthstone when under the effect of Divine Shield, to prevent easy escape from a permanent death.