the Mozilla/FF not running happened to me a time or 2...
try this-
remove the whole program again
reboot the computer
reinstall FF
try it...

oh ..in the Set Program and Access Defaults
maybe something there got checked to not let you use FF?

if still won't work can you try get it to work by going thru the My computer /hard drive & program files list?

I'm thinking something either got removed or scrambled during the AV scanning

you might do a disk clean up & defrag if needed also

and Google has a browser now
also there's one called Flock that I tried - maybe try one of those to see if they might work till you get the Mozilla figured out.