Hi samiakuma,
Sorry to hear your having a hard time with things. As the moderator R. Proffitt suggests, info about those 6 printers (make, model, connections) as well as which Linux OS-(Operating system) you're running will allow some one to help you sort these issues out and get you up and running. It's also suggested that you start a new thread/conversation regarding your issues so we don't get this thread sidetracked and off topic.
I will comment however in reference to installing Firefox dwnldd from the Mozilla site-(I'm assuming that's where you dwnldd it from). The vast majority of mainstream Linux OS's use what's called a Package_management_system to install applications etc..
A package management system is:*
...a collection of tools to automate the process of installing, upgrading, configuring, and removing software packages from a computer. Distributions of Linux and other Unix-like systems typically consist of hundreds or even thousands of distinct software packages; in the former case a package management system is nice, in the latter case it is essential.
Packages are distributions of software and metadata such as the software's full name, description of its purpose, version number, vendor, checksum, and a list of dependencies necessary for the software to run properly. Upon installation, metadata is stored in a local package database.
A package management system provides a consistent method of installing software. A package management system is sometimes incorrectly referred to as an installer.
*Ref: From Wikipedia, the free encyclopedia Package management system page.
The most common formats used are .rpm-(Redhat Linux based OS's) and .dep-(Debian based Linux OS's). These links should help you understand what they are etc..
You need to know which type your Linux OS uses in order to properly install software other than what that particular OS vendor offers in their software repository if they have one setup.
I hope this gives you a little insight about application installation in Linux OS's if you don't already understand how these work. Everything has a slight learning curve and we all have to start somewhere. Like you, I didn't "speak" computer either until others helped me and I stuck with it. Now I know just enough to get in trouble. LOL...
One thing I can tell you, is that the Linux community is composed of the most helpful bunch in the world, so don't be afraid to ask. There's jerks in every part of life, including the Linux community, but most of them are learning and frustrated as we all get at times, and this is generally the reason you'll have folks posting negatives about Linux. Just ask for help and you'll receive it. You may have to be patient sometimes for a response, but don't give up. We all have to start somewhere and even the pro's have to constantly learn new things as well to keep up with the changes in the computer world. So start a new thread here in the forums and you'll get the help you need I'm sure. Cnet sites and folks are another good bunch and there's some pretty knowledgeable folks here as well that can help you with your Linux OS issues.
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On that note I will leave this in the hands of more capable people to help you with in the new thread you start here for help. Please do so and there's absolutely no question in my mind that someone here can get you and your Linux OS working together and become best of friends for all your needs. If these folks get stump-(not likely) they will direct you to the proper place to resolve your issues. Good luck and don't give up! 
HTH.....
Regards,
BigThunder1