Favicons density in Firefox Mac 69.0.3

[MuaddibOfArrakis]

I apologise if this questions has already been asked, but now that the customisation of Firefox follows new patterns, I better enquire, before changing config parameters at will.
I found out using my search engine how to make tab text bigger, favicons bigger and most things more confortable.
What I did not find is how to reduce the inter-favicon distance and, if possible, how to vary height and width of the favicons.
Would be thankful for every hint.