accented chars not working on firefox and thunderbird

[João M. S. Silva]

After a fresh install of LMDE 2 (Betsy) accented chars do not work in firefox and thunderbird. They work in other applications.

This does not happen in Linux Mint 17.3 (Rose).

I'm using a Portuguese keyboard with English language.

$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=pt_PT.UTF-8
LC_TIME=en_US.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=pt_PT.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=pt_PT.UTF-8
LC_NAME=pt_PT.UTF-8
LC_ADDRESS=pt_PT.UTF-8
LC_TELEPHONE=pt_PT.UTF-8
LC_MEASUREMENT=pt_PT.UTF-8
LC_IDENTIFICATION=pt_PT.UTF-8
LC_ALL=