[Solved] Firefox and chrome wrong displaying characters

[Toninomint]

I have a big problem i cannot deal, I searched all possible solutions around but nothing seems work...
I think it's a system issue, cause it appears both in firefox (also after upgrades) and chromium. The strange letters đđđđđđ appears only in few web sites, like linux forums (also here), web sites supposed to have a perfect coding for my OS.
Mint 18.1 /32 bit-Firefox 69.0.3 - chromium 77.0.3865.9

[Toninomint]

After analizing the issue whit page inspector I understood it was just a font problem in my system:

the đđđđđđ disappeared when the font family box was unselected (here the browser show his default font I guess):

I made a html page with samples of the listed fonts and checked it with firefox:

After reinstalling lucida grande, all is ok (also in chromium):
I
I hope this will help other people.