Well, it seems that an appropriate custom profile is what I needed, in the end.
I have just created a new profile (XYZLUT+matrix as curves+matrix wasn’t enough) with:
- red transfer function ≈sRGB (Δ 0.97%)
- green transfer function ≈sRGB (Δ 0.97%)
- blue transfer function ≈sRGB (Δ 0.97%)
That’s not really a match with sRGB, but to my eye is close enough. I won’t bother about it, because looking at an image with a display brighter or darker than mine would cause a bigger visual change than those differences. So is it a success? I think so 
The image looks almost the same in Chrome, FFox and RT with my latest custom profile set system wide.
The sad part is that in the end I’m using a color managed solution to reach a result similar to what Chrome stubbornly keeps rendering, no matter what.
I think about it that I’ve managed to get a custom profile like an sRGB one, but with my own primaries… 
Colored: custom profile
Dashed grey: sRGB