Normally in such cases, I (suggest) uninstall Firefox, use a program like CCleaner (http://www.piriform.com/CCLEANER) to clean up the system of any residual files and then download the latest version of the Firefox installer again and install from it. This almost always works.

Though, I'm guessing there might be easier ways to deal with such issues.

Thank you but that's just about the first thing I did; uninstall, clean, reinstall, hasn't worked.

Which version of Firefox do you have?

Yesterday I was having issues with 16.1 beta - it wasn't crashing, but just freezing the heck out. I tried a clean re-install of the 16.1b, but that didn't help either. So, had to go back to Firefox 15 and that seems to work just fine.

Not sure what version, whatever is offered from the web site when I reinstalled it yesterday.

Try a clean install with the one available here: http://www.mozilla.org/en-US/firefox/beta/

Disappointed, but this didn't work either. Some additional information: I have another new problem; when I am in Microsoft Word 2007 and click on "save as" in order to save a document, I get the "warning tone", the save window closes and I have no way to save a document. This seems important because this, as well as the Firefox problem, seem to be new since Comcast did some kind of upgrade and required a router and computer reboot in order to be able to get back online. Don't know if there is a connection, but the coincidence is definitely there.

Comcast upgrade "shouldn't" cause such issues. Hmm. Do you have an updated anti-virus running on your system? If you don't yet have Microsoft Security Essentials, try installing that (it's free and pretty good) and do a complete scan, just to be sure.

Also, try uninstalling any of the latest plugins you've installed/updated on your system (like Java, Flash, etc).