I am having a problem downloading and installing something, can anyone help?

I am trying to download and install the Video Downloader & Player at ant.com. I've done it several times in the past with no problems, but I recently had to restore my computer and now when I try to download/install it, I get the following error message:

Firefox could not install the file at:
https://addons.mozilla.org/en-US/firefox/downloads/latest/8174/addon-8174-latest.xpi?src=addondetail

because: Invalid file hash (possible download corruption)-261

Does anyone know how I can fix this?

Get rid of Firefox and install IE

Get rid of Firefox and install IE

Microwin

I just realized that I am using FF 3.6.3 and apparently this add-on is only for version 3.5.7 and earlier. How do I downgrade my version of Firefox?Vic-Ferrari