Fin Spell by fluks

Usage

You can set spell checking always on or off from the settings with a blacklist and whitelist. You can set spell checking temporarily on or off on the current page either from the toolbar or from the context menu. Once you start writing, the text in an element will be spell checked and highlighted.

You can get suggested words for incorrect words by moving the text cursor on a word and pressing the right mouse button and select a suggested word from the context menu. You can also add a word to your own dictionary from the menu. Or you can add words to the dictionary from the options page.

By pressing ctrl + shift + F you can open a sidebar where highlighting of errors works for sure.