It doesn't seem to be any package to let you install it manually. You can try these:
- Install it via the marketplace inside Eclipse. Go to Help -> Eclipse Marketplace, enter eCobertura in the search field and try to install it
- Go to the web marketplace : https://marketplace.eclipse.org/content/ecobertura and drag and drop the Install button to your Eclipse
- Last resort, build the sources from BitBucket : https://bitbucket.org/account/signin/?next=/jmhofer/ecobertura/ You will need a BitBucket account. Instructions to build it can be found there : http://ecobertura.johoop.de/contribute.html
Anyway, I think that sorting out your firewall issues is probably easier than the last one...