Hmm, a rather strange Blogger/Mozilla bug – if you have an ampersand in a Blogger post, and you edit it, it automatically changes the ampersand to the HTML character entity (&). Of course, if you’ve already escaped the character, it becomes “&” and if you post and edit it again, it becomes “&” and ad nauseum.
I’m assuming it’s Blogger automatically sending out ampersands as the character entity for the textarea value, but Mozilla displaying it literally instead of translating it (which it probably should).