So, I'm gonna go with no. Foxes are in no way "dumb blonds"
The belong to the trickster mentor archetype that include a lot of mammals and avians and suxh.
foxes are often portrayed as cunning and skillfully adept mentor figures in myth and religion and should in no way be thought of as "dumb blonds" since those who chose them as a fursona most likely choose them for the positive qualities associated with them.
But that's just my drunken two cents and I'm a dumbass so who knows.