When you ran the Malwarbytes scan was there any malware found?
If there was please post the Malwarebytes log.
To find your Malwarebytes log,download mbam-check.exe from here
and save it to your desktop.
To open the log double click on mbam-check.exe on your desktop. Copy and paste the log in your topic.
When I had Windows 7 64-bit it was running just fine on 3GB of RAM, I don't see any problem with that.
I also don't see any problem using either of the two browsers. Firefox has a higher appetite for resources though.
You have Adobe Reader 9.1 and Java 6 installed. Both of these are outdated and should be updated, Adobe Reader XI and Java 8.
The following is an explanation why you do not want to have more than one antivirus installed. There is nothing wrong with either of the antivirus programs you have installed. You have paid for the Norton antivirus, so I would be inclined to use it.
IMPORTANT NOTE: Using more than one anti-virus program is not advisable. Why? The primary concern with doing so is due to Windows resource management and significant conflicts that can arise especially when they are running in real-time protection mode simultaneously. Even if one of them is disabled for use as a stand-alone on demand scanner, it can affect the other and cause conflicts. Anti-virus software components insert themselves deep into the operating systems core where they install kernel mode drivers that load at boot-up regardless of whether real-time protection is enabled or not. Thus, using multiple anti-virus solutions can result in kernel mode conflicts causing system instability, catastrophic crashes, slow performance and waste vital system resources. When actively running in the background while connected to the Internet, each anti-virus may try to update their definition databases at the same time. As the programs compete for resources required to download the necessary files this often can result in sluggish system performance or unresponsive behavior.
Credit for this information goes to quietman7.