Maybe it's because I'm using Firefox but I don't see a reply button on any thread I'm trying to participate in. The only way I can make a comment is to click on the "quote this message" button at the bottom right. That just doesn't seem right. Would it be different if I used Internet Explorer?
I am using Firefox as well and just scoot down the page to the reply box. If I wasn't seeing them I would probably run my virus scanner and if that did not take care of the issue, would reinstall Firefox.
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I get that sometimes here, other times not. You can just use the quote, select everything and delete, and then you have the same empty box as you would with reply.