Comment 1 for bug 224536

Thank you for taking the time to report this issue and helping to make Ubuntu better. Examining the information you have given us, this does not appear to be a bug report so we are closing it and converting it to a question in the support tracker. We appreciate the difficulties you are facing, but it would make more sense to raise problems you are having in the support tracker at https://answers.launchpad.net/ubuntu if you are uncertain if they are bugs. For help on reporting bugs, see https://help.ubuntu.com/community/ReportingBugs .

It's the default behaviour for UNIX systems to exclude current directory from PATH (for security reasons). In order to run files from the current directory you either have to type something like "./firefox" (starting with ./) or specify the full path for the executable.