SSD thrashing

[Phil]

I have a Lenovo T420 with 4Gb of RAM and a about 790Gb free in the / 
partition of my SSD. I also admit that I have about 30 tabs open under 
Firefox.

What would be my best course of action to prevent disk thrashing? I was 
thinking about enabling Zswap or should I just do something about the 
open Firefox tabs? Adding extra RAM might be a good idea but I don't 
know where I might buy older style RAM from online.

-- 
Regards,
Phil