One of the sentences in FAQ 72, under the RTE description, is as follows: "Additionally, the Rich Text editor is only available with entries, not comments or certain web browsers." This makes me twitch, because "only X, not Y or Z" sentence constructions should only work if X and Y and Z are all the same sort of thing, and while entries/comments works (they're both ways of adding content to LiveJournal, and thing what one would want to use HTML in), web browsers is not parallel.
So, maybe something like:
The Rich Text editor is only available when writing entries, not comments, and it may not be available in all web browsers.
...or something. Can't really think/write right now, but.