if the actual file is .php but you want it to be web-accessible as .html, you can use this:
you don't need to worry about the query string because mod_rewrite acts on the request without the query string.
this of course would make every request for an html file load it up from the php file, so if that's not exactly what you're looking for (i.e. you actually have some html files that should be used) you'd need to make it a little more complicated.
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