OK you got the real Office not the trial. You made the right move to get a new computer because all the web browsers (like FireFox) and simple applications like Picassa get more bloated all the time and need more horsepower and memory to operate. So you kinda have to buy a new computer unless you want to struggle and keep Firefox at version 5.3
I hear you, although i run FF 19 with about 80-110+ tabs open (i try to get back to them) , and OpenOffice with about 15 docs open for more editing, and Thunderbird with multiple email accounts, using a 2005 Sony PC with 2.8ghz 64bit dual core cpu, and 4gb ram and a flash drive using ReadyBoost under W/8 pro 64bit.
However, the Intel mobo will not allow more than 3.38 gb or ram to be available, which i did not know when i upgraded from XP32 bit for 29.00. So i usually have about 1gb of free ram (and a page file on a separate drive)
FF used to use a lot of cpu cycles (and after restarting it i have almost all my free ram back) until i install the NoScript extension. Sites like Amazon send it up.