Keep us posted if you're still seeing sluggishness with the editor.
For the spellcheck issue, because we're now using a WYSIWYG editor, the right click is needed to be able to pull up image and table properties, cut and paste, etc. However, there are ways to keep using browser spell checkers. If you hold CTRL (PC) or Command (Mac) when you right click in Firefox, it will treat the right click as though it's outside of the text editor. This is an extra step, but the idea was to provide the power of the context sensitive menus in the editor (to align images, add borders, color table cells, etc.) but also enable you to take advantage of browser spellcheck at the same time.