I had the same issue with spellcheck, autospell, or whatever we're calling it this week.
I noticed that on my system it seemed to be that I had no spell check anywhere, so...
I looked through system settings after reading and re-reading this post and google-ing many more to find a solution...And, well, it's in system settings.
I found Preferences > Language support on the start menu (not in firefox, but in the lower left as-in-on-the-task-bar start menu) and opened it.
It ran an auto check on start-up and told me not all packages had been installed, and asked if I would like to complete the installation.
Provided root P/W when prompted by the app and it completed the language pack installs.
I've checked on a couple forums and here also - anything misspelled now gets a red underline and right click provides spelling options.
In Slackware I think the package is called aspell, I did a <sudo wget -i aspell> from the command prompt just to check and it verified that my system was up to date, so apparently aspell is a Linux common package.
I realize this is a few months after the O/P brought it up, but maybe this will save someone else the frustration.
Other things to check are dictionary from the office menu tab, and for anything else if you don't see what your looking for right off you can always use the search box at the bottom of the menu > applications screen.
Hope that helps.
(I might have found this sooner but I was too busy with grub2 configuration and learning patience).