Douglass was an advocate for women's rights, especially suffrage, and a feminist ally to many of the most significant feminist activists of his era, such as Elizabeth Cady Stanton and Susan B. Anthony. However, his relationship with the established American women's rights movement, and his relationship to women in his own life, was much more complex than that statement implies.

Douglass initially moved in abolitionist and reform circles connected to William Lloyd Garrison (the Garrisonians, noted for their staunch devotion to immediate emancipation and religiosity), and reform movements of the mid-19th century frequently overlapped. Many of these reformers - Douglass, Garrison, Stanton, Anthony, as well as others like Lucretia Mott or the Grimke sisters - were not only abolitionists but also supporters of women's rights, the temperance movement, and often had ties to other, somewhat radical ideological positions or religious movements, like Transcendentalism or Spiritualism. While Douglass never identified with either of those movements, he did exist in this milieu, and frequently worked alongside women who promoted abolitionism.

Douglass was present at the seminal feminist event of the 19th century, the Seneca Falls Convention in 1848. He was the only African-American to attend, and not only were many (perhaps most or all) of the attendees abolitionists, the convention itself was born out of an earlier slight at an abolitionist convention. In 1840, the first World's Anti-Slavery Convention had been held in London, and despite women petitioning to speak, their pleas went unheard and they were only allowed as spectators. Seeking to redress this and other grievances, the Seneca Falls Convention drafted the Declaration of Sentiments, which notably called for women's suffrage. Douglass was noted for speaking on behalf of the inclusion of this clause, which had been hotly debated, and he further advocated for women's rights in his newspapers, The North Star and Frederick Douglass' Paper. After the Civil War, he famously broke with Stanton and Anthony over the voting rights of Black men. Douglass, and other former abolitionists (many but not all of whom were also men), believed that it was crucial that Black men be given the vote, and that holding out for women to be included in a potential voting rights act (eventually the 15th Amendment) would only weaken support for it. Others, former allies, disagreed, and resorted to some racist attacks on Black men to shore up the case for white women being given the vote (Black women were often completely ignored in discussions of suffrage.) This caused a rift which led to Douglass, who never abandoned his beliefs in women's rights, becoming largely aloof from the developments in the feminist movement of the later 19th century, though by his death in 1895 he had mostly reconciled with both Stanton and Anthony.

However, in his biography on Douglass, David Blight makes the argument that his personal life may not have been so egalitarian. Douglass' first wife, Anna Murray, was several years older than him and born free, and who was instrumental in helping him gain his freedom and in supporting their family while Douglass toured a punishing lecture circuit on behalf of abolitionism, which took him across much of the northeastern United States and to Europe. Douglass, however, rarely spoke or wrote about his wife, and she was an almost invisible presence to those who knew him. He likely also conducted at least one affair, which involved allowing the woman in question (Ottilie Assing) to live with his family, and while nothing is certain about Anna's feelings on this, I personally can't imagine Douglass was taking into account her opinions on the matter. While we know Anna supported abolition, she was not a public person who worked alongside Douglass. His second wife, Helen Pitts, however, was a fellow activist and a feminist, and Douglass initially grew close to her because of their shared beliefs.

I hope the digression into Douglass' personal life wasn't too distracting, but I think it demonstrates that while Douglass held sincere beliefs on women's rights, he also didn't necessarily apply those beliefs to his everyday life, at least with Anna Murray Douglass. But since you asked for his views on women, period, I figured I'd add that in, especially since it intrigued me while I read Blight's biography Frederick Douglass: Prophet of Freedom, my main source for this answer.