Winter is always a challenging time to interact with wildlife in NJ. Not only do you have the obvious, extreme cold, fewer daylight hours, but many of the animals that might pique your interest are either sleeping underground or vacationing down south.
But foxes are VERY active in winter. They do not hibernate and the NJ fox mating season is January-February. During this time, and potentially no other time as they are not pack animals and don't usually tolerate company, you just might catch a glimpse of more than 1 simultaneously. Its also a great time to spot them against the typically leaf-covered forest floor as they tend to stand out clearly in the snow. On top of that, post-accumulation is the optimum window to catch them with your camera as a snowy background is hard to beat.
If you go out, don't forget the iron-powder air-activated ("Hothands" is a well-known brand) hand-warmers. I just read a tip about these. They should be placed on top of the hands in the gloves instead of at the palms. The skin on the top of the hands is thinner and the blood flow is greater which aids the performance of these micro blast furnaces.
So break the cabin fever, get out and catch some NJ wildlife this winter.