I am certain that it is against their Terms of Service.

I'm not so sure. I suppose it'll take a representative of the company to interpret what was really meant, but agreeing "not to access the service by any means other than through the interface that is provided" doesn't seem to me to be a promise to use an interactive browser.

Afterall, they don't provide a browser, so that must not be what they mean by "the interface that is provided."

I think the interface they provide is defined by their web servers, not by the various clients that may be used to access them.

Besides, I really doubt that Yahoo cares whether you suck down their pages using Mozilla or something hacked up with perl and LWP. The fact is that they are not going to lose much revenue anyway. The number of people that do this sort of thing is relatively small; the lower page views probably don't translate to much lower click throughs; and your mail accounts with them have other value (e.g. you agree to receive their spam.)

-sauoq
"My two cents aren't worth a dime.";