The grid lines in firefox do not appear to be antialiased which can be seen by the gaps and corners in the screenshot below. The grid lines in the chrome screenshot look totally fine.
I'm using firefox version 68.0.1 on Sierra.
Screenshots taken from the codepen example on the docs
Firefox

Chrome

specs
MacOS Sierra 10.12.6
MacBook Pro (15-inch, 2017)
Graphics
- Radeon Pro 555 2048 MB
- Intel HD Graphics 630 1536 MB