Is this problem just on Inspector news? or is it also happening on other web sites?

Firefox is a great browser. That said it is a HUGE memory hog. The more tabs you open and close the more memory it uses and it does not release it all back to be used again. Your system could be low on memory which causes lag or the possible "not responding".
Try this
-bring up Windows task manager (control, alt, del)
-click view tab
-click "select columns"
-check "Virtual memory size"
-click OK
-click the VM size column heading twice which will show the highest user first.
You now can track the virtual memory size on task manager, which is actually the page file on the hard drive that Windows uses when it runs out of memory. You will also see the memory usage go up as the VM size increases. It will keep growing until Windows needs more and thats when your system really slows down.
2 solutions, reboot, or just shut down Firefox and start it up again.
Firefox will normally (depending on number of tabs open) use 80,000k. When you get up to 200,000k (depending on your page file and amount of memory) you may start noticing problems. I just checked mine and I am using 250,000.
Well all for now, I have to shut down Firefox.

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