hi Mrconstant, this sounds like a problem possibly caused by adware on your pc.

1. please go to the firefox menu ≡ > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc).
2. also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there.
3. finally, run a full scan of your system with different security tools like the free version of malwarebytes & adwcleaner, which are specialised in adware and browser hijackers.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

See also:

• http://malwaretips.com/blogs/?s=shopathome

Mrconstant said

I sign in via Firefox. Sometimes I get the Firefox home screen sometimes I get taken straight to Yahoo for my mail. The Yahoo menu bar show shows "Shop at home" and all their related junk. As I start to read my e-mails, Shop at home takeover my screen with some dating site called "our time". I've asked to be deleted, but they think I'm a member. I am not and never have been. I don't have this problem when I log in via Internet Explorer, Safari, Goggle Chrome...Just Firefox. I also noted that I need to re-sign in often with Yahoo even when I check "keep me signed in"...this also only happens when I use Firefox. Both problems just started recently. Help!

Thank you very much. I followed the correction advice and the problem was solved. I have not downloaded the Malwarebytes or Adwcleaner yet, but plan to. Thank you again.