Is it "quit" or "quitted"?

What is the correct (grammatical) simple past and past participle form of the verb quit? Is it quit or quitted?

She quitted her job. (She has quitted her job.)

She quit her job. (She has quit her job.)

I would use quit, as it is more readily understood by people. Dictionary.com indicates that both are plausible. Merriam Webster says the same.

Looking through Google books, quitted seems to be used synonymously with left, e.g.,

Plato quitted Athens, where he was adored as a god ...
I quitted Manchester, I quitted Mrs. ++++++++, I quitted ++++++++ hall ...
... you have not quitted the path of virtue ...

Although this usage seems to have declined markedly. This can be seen in a Google NGram, as found by FumbleFingers:

The OED records both as alternatives for the past tense and the past participle.