The first abolitionist society in the colonies was formed in Philadelphia in 1775.
In his (Benjamin Franklin) later years he became vocal as an abolitionist and in 1787 began to serve as President of the Pennsylvania Society for Promoting the Abolition of Slavery. The Society was originally formed April 14, 1775, in Philadelphia, as The Society for the Relief of Free Negroes Unlawfully Held in Bondage; it was reorganized in 1784 and again in 1787, and then incorporated by the state of Pennsylvania in 1789. The Society not only advocated the abolition of slavery, but made efforts to integrate freed slaves into American society.
You will observe that the title of the organization when it was founded refers to Negroes Unlawfully
Held in Bondage
This was prior to Lexington and Concord by 5 days. So this was an issue at the time of the Revolution. How much of an issue, I don't know. I do know that General Lafayette became a member of the Abolitionist Society in Philadelphia before he went back to France and that he proposed to Washington that slavery should be abolished here. Perhaps that is why Washington's slaves were manumitted in his will. It is well known that he thought very highly of Lafayette.