Hi Dede..
Ok ... raspbian is a debian-based linux distro .. so ubuntu instructions and apps (apt) are valid for raspbian as well.
You can download a stand-alone version of Firefox directly from www.mozilla.org ... it will be a zipped file known as a tarball (tar.bz2). Once downloaded, right-click on the tarball and select 'extract here' and a folder should appear called firefox. This folder will contain the browser and everything it needs to run without accessing your system files - hence stand-alone (everything except flash, of course)
Pepperflash will only work in Firefox IF you have the freshplayer plugin which should be available from the rasbian repository (repo). If it is not available (or you can't find it) then you cannot use pepperflash so you will have to use the ordinary flash for firefox i.e. npapi .. not as good, but it will do. Just select the apt version for debian/ubuntu at the Adobe flash download site if this is what you need to do.. it should auto-install.
FYI - later this year (october most likely) I will post full instructions for Chromium - this may be better for you as it does not need any plugin to run pepperflash...
Lastly - sudo will only work if it has been set-up correctly on your system. Personally, I never bother with sudo - it is too much hassle.. it is easier to sign in as root user (command is 'su' ... then enter the admin/root password) this changes the prompt from $ to #. Just remember to sign out 'root' when you are finished by typing 'exit' at the #.
P.S. Mozilla is the name of the organisation - Firefox is the name of their product, the browser