The last time I enabled fractional scaling in Sway, I quit using Sway and Wayland in frustration and moved back to i3. Firefox, and many other applications, just don't behave appropriately when scaling (integer or fractional) is enabled. There are also bugs open on the Sway github issue tracker for this so it's not like this issue is restricted to just me.

So it's best to have a laptop which needs either 100% scaling or 200% scaling, nothing in between.