iMac 21.5" 4k Screen Colours Washed Out

I bought a new iMac 21.5" 4k screen for my web design work.

I noticed that the way Safari renders colours is completely different from the way Chrome and Firefox does. Colours in Safari appear dull and washed out, while in Chrome and Firefox colours appear more saturated.

I checked my iMac's colour settings under "settings > display > color" and it's set to the "imac" colour profile. The funny thing is, if I set the iMac's colour profile to sRGB, all of the colours on my screen become very vivid and consistant between all of the browsers.

It seems to me that Chrome and Firefox are forcing some kind of sRGB colour profile while pretty much all other apps follow the 4k screen's wider gamut iMac colour profile. In any case, I can't understand why the sRGB colours are so much more vivid than the iMacs wider gamut profile and why Chrome and Firefox behave differently to other apps in their rendering of colour.

Searching online I can't find a single mention of this issue, which has completely perplexed me. Is anyone else having this problem?