The English language is beautiful, strange and quirky.

"Furniture" is a word that's supposed to refer to things that you CAN'T count. So it's neither singular nor plural.

I'm not sure if it can be considered a "collective" sort of noun, something that refers to MANY things, but taken together as a WHOLE. "Furniture" in a way, is an abstraction. It refers to more to an idea rather than actual objects. (I could be wrong here so anyone who can correct me, just in case, please feel free to do so.)

So you can't say "These furniture." Better to say "The furniture" as in "I'm going to re-arrange the furniture." You can also say, "What am I going to do with all this furniture? I either sell some of them or move to a bigger house!"

You can use the word "furniture" in the singular sense if you say "This is a nice piece of furniture."  In the plural sense, you can say, "I'm getting rid of these ugly pieces of furniture." or "She's a beautiful woman but lacking in taste. I went to her house and saw several ugly pieces of furniture."

The word "food" is a related case. You can say "food" in a general sense, again, collectively. "I like good food." means you like food -- in general -- that for you is delicious and well-prepared  following your own taste.

You can say "foods" if you are making distinctions between several types of food. For example: "There are healthy foods and foods that could actually make you sick." 

Or you can say, "I'm not really a big fan of Asian food (general, collective). But among the foods (meaning, the different types of food from the Far East) of the Orient, I like Japanese food (general, collective) and Chinese food (general, collective) best."