I have recently used my portable version of Firefox on another computer which already had Firefox on it's HDD. The computer I used also had AVG Free AntiVirus installed on it with AVG Security Toolbar installed on it.
When I started Firefox portable from my USB key, The AVG security toolbar was installed on my version of Firefox portable. But when I went back to my home machine, the toolbar was no longer there.
Why did this toolbar install when it was not installed already. And if that happens, how do I know that my personal information from my FFOX portable was not left on the machine I used?

