I do not have a proper answer and do not use Mint, but no one else has answered yet.

I just wondered whether the OS is able to offer options from Libre Office's hunspell dictionaries what have you got there ? Could the Libre Office install explain some of the additional options ?

I suspect that when firefox is preinstalled with Linux Mint, it is also preconfigured in a specific way. Perhaps removing firefox and installing it directly from Mozilla instead of using apt-get install might improve this and other issues.

Just a wild guess.

The dictionaries and languages are probably in your package manager.

Thanks, where would I find the package manager? Is it part of Firefox or the operating system?

Btw, I have the same issue posted over at Linux Mint Forums, providing some clues: http://forums.linuxmint.com/viewtopic.php?f=47&t=190115

You can check these locations for globally installed dictionaries:

• /usr/share/hunspell/
• /usr/share/myspell/

jonas-e said

Thanks, where would I find the package manager? Is it part of Firefox or the operating system?

Package manager is a general term to refer to a place that you can manage the install, updates and the dependencies of say .deb or .rpm packages that you install on Linux depending on the Linux distro.

http://en.wikipedia.org/wiki/Package_manager