Well, it seems that in the end I’ve found a workaround, thanks to your comments: it seems that as in other situations, the users don’t have the means nor the right to tweak something Google has coded, and we just have the right to accommodate to a given software (
this somehow reminds me the bad old days of Micro$oft). (Yes, I know I can edit the Chromium code, but I’m not a programmer…)
Now to the «solution»:
- Chrome uses a pure, canonical sRGB profile. That’s it. Like it or not.
- Firefox uses by default the system color profile, which unless you have a high end display, will be something close to an sRGB color profile
- my calibrated display has a bit wider color profile than sRGB (at least with a couple of primaries), thus, I can see better colors with RT, Firefox, XViewer, …, but not in Chrome (that keeps showing images with an sRGB profile)
- after setting my display to use a canonical sRGB profile and rebooting, I get this:
(left side: Chrome, center: RawTherapee, right side: Firefox)
If you look really carefully the renderings are not exactly the same, but to me they are close enough.
The sad part is that Google prevents me to make use of all the colors my display is capable of rendering 
It feels like the old story that somebody knows better than me…
Thank you all for your helpful comments. I really appreciate them! 