CentOS - Oct 2019 - Have "system"/Hunspell dictionaries stopped working in CentOS 7 Firefox?

Until quite recently, multiple spell-checker languages were available in 
Firefox on my CentOS 7 system. (They could be selected from
"Languages"
under the right-click menu in text boxes.) After a recent system 
upgrade, there is only "English (United States)".

I don't think I had installed any extra Firefox dictionaries as such, 
but the "global" spell-checking support is set up to support a few
extra
languages via hunspell-<lang> software packages. I believe Firefox used 
to be able to pick these up - probably through a link from 
/usr/lib64/firefox to /usr/share/myspell that the CentOS firefox package 
provides.

Did I get that right? Has the mechanism stopped working? Is there any 
way to re-enable the system dictionaries?

Note that I get all the expected dictionaries in Thunderbird, which 
appears to rely on a similar hack.

My Firefox is "firefox-68.1.0-2.el7.centos.x86_64".

Thanks.

- Toralf