I don't wear chaps,but I'm not cutting firewood. Most of my day is using a smaller topping saw. In addition,my lower body is somewhat protected by the bucket....or I'm climbing,and chaps would severely restrict my mobility
That said,I do a number of things I don't recommend anyone else doing. Plunge cuts come immediately to mind.
Also,most of my work pants have a small hole near the front pockets. It's from saw chains "winding down" when I pick up and carry a bigger saw saw after a cut when I'm on the ground. I use the chain brake ALMOST religiously but sometimes I'm "in the zone",in a hurry,and wreck another pair of jeans.
I DO recommend chaps,especially for the continual cutting that firewood entails....If you're doing a lot of cutting,I'd guess the odds to be about 1 in 3 that you'd be using the Stihl 290,with a 20" or 24" bar. That's a decent sized saw with a fair amount of power. There's a good chance of kickback,or slipping,or something in the course of cutting multiple cords of wood,and you'd be glad for those chaps then. I know of 3 accidents where chaps would have prevented injury - 2 by landscapers who were very familiar with chainsaws but didn't use them all day,every day. The third was by a friend with a competing tree service.
Comfortable ear protection. ...I wear safety glasses because I have to be able to see someone approaching my "drop zone" from the corner of my eye,or other hazards that I'm not really look at (or for). But I visit the eye doctor several times each year to have wood chips removed,and a bothersome chip in my eye that doesn't require a doctor is an almost weekly occurrance (including today)....Safety glasses don't keep out those little bits of "dust" on windy days,either.
I recommend the mesh face shield AND safety glasses. You might as well get the hardhat with face shield. Kickback HAS occurred that parted the victim's hair. And skull....Some of those have ear protection built in.
Good leather boots. Don't ever use a chainsaw wearing tennies. Gloves are good too - at the very least they dampen the vibration of the saw. I almost always wear them when using bigger saws.
My accident happened 8 years ago. I was using a topping saw 1 handed,above my head,holding a branch with the other hand. 60 stitches to that "other" hand,and I was lucky...Don't get too comfortable with that saw. I guarantee you that a chainsaw does not cut flesh like a knife. It's more like a meat grinder.