This is normal. IRS does not run the SSL site on that domain.

You get the same error at https://www.whitehouse.gov/ for example.

Normal? Why would a server "... identifying itself as a248.e.akamai.net" handle that traffic?

That part of the IRS site is not on Akamai's secure network. Its for HTTP-only sites that don't care if a user gets a scary browser warning before clicking through it, and getting to the site with a mismatched cert.

... because it's a CDN apparently. Huh!

Normal or not, this is terrible user experience.

I attempted to find a online form, and was directed to https://sa1.www4.irs.gov/irfof/lang/en/eiaTPstatus.jsp.

It looks like www.irs.gov is not used for secure connections.