What's it supposed to mean now?

Effervescent’s primary definition is a chemistry term referring to air escaping from liquid in foam, bubbles, or fizziness and the etymology connects back to the Latin verb fervere (to boil). There is already a secondary definition, which I’m guessing is what the OP of that post was using, meaning like “a bubbly personality” or vivacious, enthusiastic, etc. The idea of the post is that his character would look at something small, slow, quiet, (boring) like a snail and just interpret it as this lively wonderful being-- which tracks with the common understanding of Bella as a character lacking much personality or liveliness and Edward finding her to be the same way. But, with the post being meme’d, the connotation is shifting from a sort of descriptor of bubbly personality to the idea of finding something incredible or awe inspiring (with a layer of irony added in that it’s something not usually regarded as incredible or awe inspiring). The usage and thus the definition is gradually shifting in a similar direction to “fantastic” or “awesome” where the original usage has taken a back seat to a much more common usage of hyperbole.