I just went into my hotmail through Internet Explorer and it worked fine. I think the problem is with Firefox, which I'm going to delete and re-install. Meanwhile, if you're interested, here's what I originally wrote in response to your post:
I cleared my Internet files as you suggested, including the cookies, the cache, browsing history and active log ins. That had no effect. I also tried entering "optimize browser settings" into the Firefox help search bar, but there was nothing found for that entry.
I don't think this is a temporary issue since it's been going on for more than a month. And, while it doesn't affect every single email, I don't think it's only on the recipient's end, since I can't open my own emails that have Word attachments when I go into my sent file and try to open them myself. It doesn't matter who I send them to.
The only time I was able to open one of those emails with a Word attachment was when I sent it from another computer. So I still think it's something with my home computer.
Rob