Thanks for all the comments!
Wow, they take their Mayonnaise seriously in the Netherlands, they have a law that says it must be at least 70% fat and 5% egg yolk?
Yes, that's true! This is the mayonnaise shelf (and part of the ketchup and "curry ketchup" at our local (not so large) supermarket. The question if "frietsaus" counts as mayonnaise is widely debated. I'm on the side that it doesn't count; the taste is much blander. So yes, we do take it very serious XD. I have seven different mayo's in my home at the moment (if you count frietssaus; two kinds of "frietsaus" (which my girlfriend likes more), truffel mayonnaise, Belgian mayonnaise (which is a bit more sour), Calvé brand, "Zaanse mayonaisse" and "Brander mayonaisse" (which is a mayo - mustard blend). Most of the time I mix it with curry ketchup and best of all with chopped onions.
We even have something called "American mayonnaise" which is nothing like American mayonnaise but a kind of "frietsaus" with some kind of herbs in it that is sold at McDonalds instead of mayonnaise here (although they have added mayo on the menu recently). It's not white but yellow, I have no idea what's in it. (it's the one with the American flag on in on the second photo)

We would need to know more about what kind of fries you get in the Netherlands, are they:
- Super skinny fries
- Thick cut steak fries
- Crinkle cut fries
- McDonald's Style fries
- Skin off
- Skin on
- Etc.
Do they have:
- Salt
- Garlic
- Other seasoning
Mostly the thicker kind without skin (I like them with skin though). But in a lot of places (both restaurants and the takeout places centered around fries and deep fried snacks) you get to choose between the thicker and the skinnier kind. But even the skinnier kind are not as skinny as the mcdonalds fries mostly and not as thick as the steak fries (you do get steak fries in some restaurants though). Mostly cubical in shape but sometimes a bit rougher cut. McDonalds fries seem to be a bit thinner and more salty than our usual kind. They sell the crinkle cut fries at stores but haven't seen them in any restaurants ever.
As for seasoning; mostly salt or not seasoned, but we do have "frietkruiden" (or "fries herbs" literally translated) in stores which is a seasoning specifically for fries (with salt, pepper, paprika, musterdseeds, ginger, coriander and a few other herbs)
Most of national cuisine on the lower end (am I saying that right?) is potato-based (hotchpots of mashed potatoes and vegetables, don't like that much to be honest) or deep fried. A lot of variety in deep fried snacks mostly with meat croquettes, different kind of sausages, etcetera. Most of those snacks are eaten with mayonnaise (often in combination with other sauces) too.