What is the similarity of both Daisy's moral ambiguity in The Great Gatsby and Abigail's moral ambiguity in The Crucible?

Daisy and Abigail both display immorality through their affairs.
Nick helps Daisy and Gatsby reconnect after many years. While we don't know exactly what goes on between them, we do know that Daisy begins to spend lots of time with Gatsby:

“I hear you fired all your servants.”
“I wanted somebody who wouldn’t gossip. Daisy comes over quite often—in the afternoons.”

Gatsby has fired his servants to get rid of witnesses to the goings-on between them. Daisy is married and should not be having secret meetings with another man.
On the other side, Abigail sleeps with a man whom she knows is married to someone else.

Abigail: I know how you clutched my back behind your house and sweated like a stallion whenever I come near! Or did I dream that? It’s she put me out, you cannot pretend it were you. I saw your face when she put me out, and you loved me then and you do now!
Abigail: A wild thing may say wild things. But not so wild, I think. I have seen you since she put me out; I have seen you nights.
Proctor: I have hardly stepped off my farm this sevenmonth.
Abigail: I have a sense for heat, John, and yours has drawn me to my window, and I have seen you looking up, burning in your loneliness. Do you tell me you’ve never looked up at my window?
Proctor: I may have looked up.

Daisy and Abigail are also both liars with blood on their hands. Abigail lies about what happened in the woods, and she claims innocent townsfolk are witches. Her fabricated tales of witchcraft result in the death of people she claimed to be witches. Daisy drives the speeding car that hits and kills Myrtle Wilson. She does not even stop. Her carelessness causes immense pain. Daisy does not take responsibility for this, allowing people to think Gatsby was the driver.
We can look at how the two women are pushed into their lies by the circumstances and people around them. While this does not absolve their sins, it does explain them to a certain degree. For example, during a fight, Gatsby pressures Daisy to claim she never loved Tom, which isn't true:

“You never loved him.”
She hesitated. Her eyes fell on Jordan and me with a sort of appeal, as though she realized at last what she was doing—and as though she had never, all along, intended doing anything at all. But it was done now. It was too late.
“I never loved him,” she said, with perceptible reluctance. . . .
“Oh, you want too much!” she cried to Gatsby. “I love you now—isn’t that enough? I can’t help what’s past.” She began to sob helplessly. “I did love him once—but I loved you too.”
Gatsby’s eyes opened and closed.
“You loved me too?” he repeated.
“Even that’s a lie,” said Tom savagely.

We can see how Daisy is pressured by both men. Gatsby is happy to take the blame for Myrtle's death in order to protect Daisy.

“Well, I tried to swing the wheel—” He broke off, and suddenly I guessed at the truth.
“Was Daisy driving?”
“Yes,” he said after a moment, “but of course I’ll say I was."

After Wilson kills Gatsby, Daisy sees no reason to correct the lie. This lie is for self-protection.
Abigail's witchcraft lies, too, begin as a form of self-protection. Initially, she denies practicing witchcraft, but she sees that the adults in the town will not give it up. So Abigail takes their suspicions of witchcraft and uses them to put the blame on others in order to save herself.

Hale: Why are you concealing? Have you sold yourself to Lucifer?
Abigail: I never sold myself! I’m a good girl! I’m a proper girl!
(Mrs. Putnam enters with Tituba, and instantly Abigail points at Tituba.)
Abigail: She made me do it! She made Betty do it!
Tituba, shocked and angry: Abby! . . .
Hale: You have sent your spirit out upon this child, have you not? Are you gathering souls for the Devil?
Abigail: She sends her spirit on me in church; she makes me laugh at prayer!
Parris: She have often laughed at prayer!
Abigail: She comes to me every night to go and drink blood!
Tituba: You beg me to conjure! She beg me make charm—

We can see in this scene how there is pressure on Abigail, and so she pushes the blame on Tituba.
Although it does not make it okay for Daisy and Abigail to lie, we can see how their lies come out of pressure from others and an attempt to save themselves.