Thier is a Firefox Addon call Spell Checker
https://addons.cdn.mozilla.net/user-media/addons/11259/spell_checker-1.3.2-fx.xpi
Spell Checker checks for spell mistakes in a webpage.
With the proper macro Spell Checker may work with K-Meleon 74.0 and K-Meleon 75.0 Beta 1 to check websites for spelling mitakse.
It might able to work with other things than just websites in K-Meleon if macro is worked right it maybe able to check like source code and typed text in the browser.