How to find the cause of firefox freezing?

Question

Mozilla Firefox

The CPU is enough for work, the memory is also enough.
The multisession works - two windows.
It began to hang shamelessly - one of the browsers just hangs (and - without load).
We see in the processes of the hung user: -one or more firefox threads are waiting for the completion of network I / O.
I don’t quite understand - is he trying to write / read to the disk or outside?
2 GB of memory and percent - previously the same worked perfectly.

Answer 1

try the ESR version without extensions

Answer 2

there are sites that hang the system,
eat up all the memory + swap (I still don’t understand how to treat it, except for killing the process, if you have time :)
How to solve problems with memory and gluttony of browsers / applications?