Some sites don't display the "t" in Firefox?

Question

Mozilla Firefox

Recently upgraded Linux Mint from 19.2 to 19.3. Also Firefox 72.0 -> 72.0.1 -> 72.0.2. Didn't notice when the problems started.
List of known problem sites:
social.technet.microsoft.com
cyberforum


Where to dig?
PS: It's not about additions.

Answer 1

The problem affects not only Firefox, but also Google Chrome. And just Firefox helped me. I went to a site where the letters are displayed incorrectly. I selected this fragment in developer mode (F12) and looked at what font he applied, it turned out to be Lucida Grande.
I solved it this way:
Installed Font Manager
Disabled Lucida Grande, then saved the settings
Restarted the programs