In the home, furniture means items like tables, chairs, beds, wardrobes, etc.
A more generic term is furnishings .
Curtains and cushions, etc, are called soft furnishings .
Sewing accessories are sometimes called notions by hobbyists, but it isn't a well-known usage.
furnishings noun [plural] ​ the furniture, curtains, and other decorations in a room or building:
Bathroom furnishings are in the basement of the store.
Cambridge Dictionary
ell.stackexchange.com/users/40588/Mick
The general term for those things, among people who sell and install curtains, etc. , is 'hardware'.
When you move from one home to another, you would say: All the hardware for the living room curtains is in that box.
When you buy new curtains, you would ask: Will my existing hardware work, or do I need to buy new stuff?
When you paint a room, you would say: I'll have all the hardware down off the walls tomorrow morning.
Hardware
(MW, definitions 1 and 2) ware (as fittings, cutlery, tools, utensils, or parts of machines) made of metal major items of equipment or their components used for a particular purpose
That's the specific sense of the word.
What's confusing about it is that a 'hardware store' sells a lot more than just hardware, including lumber, plumbing supplies, furniture, appliances, etc.
Some someone who is not an interior designer, carpenter, builder, or painter might refer to a piece of lumber as 'hardware', since they bought it at a 'hardware store'.
Some people also refer to those pieces as 'fixtures'.
Fixture
(MW definition 2a)
something that is fixed or attached (as to a building) as a permanent appendage or as a structural part
ell.stackexchange.com/users/41970/John Feltz
The word furniture cannot be used for all accessories and fittings but can be used for some.
The source you provided gives an example of rifle fittings (rifle furniture) and I would give an example of door handles, locks and hinges, referred to as door furniture.
There is also street furniture such as street lighting, signs, benches and litter bins
ell.stackexchange.com/users/44824/Chris Rogers
What you have pointed to is a definition that explains how to understand a word when it is used in a certain way,but not when you can use the word in that way.
The term "furniture" has a well-known technical meaning in printing,for example.
It means certain pieces that are fit among or around thepieces of movable type in an old-style printing press.
But I think one would not use "furniture" to refer to other small accessoriesor fittings (such as a composing stick) that are used to assemble the typeor operate the press.
If you search the Web for "rifle furniture," you may find anumber of links to manufacturers or sellers advertising certain parts ofrifles.
(The word seems to correspond to the stock of a rifle orparts that serve the function of the stock.)A rifle has other accessory parts (such as sights) that appearnot to be "furniture."
A Web search for "Mac furniture" is not as successful.
That usage may have been intended to work by analogy, comparing the assignment of functions of graphical objectsin software interface to the placement of pieces of furniture within a room.
So the question is whether "furniture" would correctly be understood when used to denote things such as curtain hooks.
Unless you have observed multiple uses of the word in that wayby people whose business it is to deal with such things ascurtain hooks and rods, I would not advisetaking the risk of using it that way.
The risk of misunderstanding is large, sinceyou mean to speak of things that are part of thegeneral furnishings of a roombut are not among the things most people would think of as furniture.
ell.stackexchange.com/users/10002/David K
No, you can't use "furniture" as a general term for any accessories or fittings.
household furniture like sofa, table, chairs, book shelves this kind of product referred as furniture.
If you are still confused check out this Wikipedia article FURNITURE
ell.stackexchange.com/users/47721/user65083
Can the word "furniture" be used as a general term for accessories and fittings, for example, curtain accessories (hooks, brackets, rings)?   Furniture: the small accessories or fittings that are required for a  particular task or function ( source )
Furniture as a general term for curtain accessories
ell.stackexchange.com
<word-usage><synonyms>
ell.stackexchange.com/questions/112778
ell.stackexchange.com/users/44895/Yulia
Furniture may not often be used in this context as the risk of misunderstanding is great. Other suggestion for this would be "hardware" or "fittings". The word "furniture" can be used only for some accessories/fittings but there is a big risk of misunderstanding if it is used, since it is reserved for more generic house furnishings such as a sofa, a bed, etc. Instead, the terms "furnishings", "hardware" or "fixtures" are used by professionals.
There is a big risk of misunderstanding if the word "furniture" is used, since it is reserved for more generic house furnishings such as a sofa, a bed, etc. The terms "furnishings", "hardware" or "fixtures" are used by professionals. The word "furniture" can be used only for some accessories/fittings.