Chrome has a bunch of bugs related to font-rendering on Windows, e.g. https://crbug.com/414307. I'm not sure why switching to DirectWrite didn't just fix these bugs, but subjectively appearance-wise on Windows, Firefox > Edge > Chrome.
Mozilla is experimenting with which default is preferred by fresh install users right now, so users on this thread may have different initial defaults. I don't think that there are plans to change the default for existing users.
How? I was looking for this last week and couldn't find any settings that worked. Nothing relevant in about:config, and the toolbar customization shows the search bar there until I close customization.
Go to customize mode and hover your mouse pointer on the search bar. You'll notice that your mouse pointer turns into a hand, then just drag the search bar and drop it into the center of the screen (blank space).
They even got rid of that search bar, haha.
Only fonts and the scroll bars seem a bit old school compared to Chrome.
Also, WhatsApp Web keeps logging me out.