It sounds like you were using a theme that is not compatible with version 7. Have you checked the add-on site for an updated version?

Note - there are known security issues with running old versions. You can find version 6.0.2 installer at ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/6.0.2/

Haven't changed themes in years! Used link, but not sure what to click on. Was 6.0.2 the one that has the blue kitties? That's the one I'd love to get back.

The default Firefox theme does not have blue kitties. That is either a 3rd party theme or Persona.

If you go to Tools -> Add-Ons and click on Appearance what is listed?

Thank you so much. You're my hero!!!