Hmm.. You have four instances of firefox.exe?
Generally, an instance of an application (eg. firefox.exe) is
captured on your Task Manager for every attempt made to launch that
application. So, that means something(s) on your computer is trying
to launch your browser (for three times) even though it was already
launched. As a result, Task Manager will just "pool" these
processes together and "share" the RAM.
As to what actually caused this, I have no idea. It may be malware,
or it might be driver conflicts. But, since you are using mIRC, Bit
Torrent, and somewhat of an online gaming platform, I would suggest
you to scan your computer for potential malware. If nothing turns
up, try updating all your programs to resolve any potential
"conflicts" in your system.
