Buster: Firefox-esr: can't get spell checker to work

[local10 <local10@tutanota.com>]

Hi, 

Does the spell checker works in Firefox-esr in testing? It does not work for me in Buster but  was working fine in Firefox-esr 52.8.0esr-1~deb7u1 in Wheezy.

Any ideas? Thanks

Preferences > Advanced > [X] Check my spelling as I type (checked)

layout.spellcheckDefault=2