Hi @broberto,
Thank you for reporting this and welcome back to the forum 
Not sure if this counts as a bug but it was reported to Firefox 13 years ago and the ticket is still open: 627771 - Add dithering to gradient color transitions to address banding in 24-bit "truecolor". Chrome uses dithering which gives radial gradients that “smooth” effect.
But I’m tagging this as “no bug” since it’s not related to Bricks.