After playing around with a couple of spell-check-type plugins for WordPress, the bright idea hits me to find one for Firefox instead. (Honestly, I should’ve thought of this sooner … senility I tell you!)
I remembered seeing a post on Extensionsmirror.nl about a plugin that would spell check textarea and input values.
It took a short bit of work to get installed and properly configured. (Had to use the install wizard on the site in the end because I guess I screwed up the manuall install somehow … oh well, whatever works!) And now I can spell check my posts BEFORE submitting them. :D