Firefox runs almost 90% cpu after login screen(I didn't open any firefox window, it can only be seen in system monitor)

Please do post your RAM memory and cpuconfigurations that will let us know if you need more memory to run ubuntu smothly on your computer.Any Devloper here can fix this with bash scripting to flush out firefox bin process when not in use.

hi, my laptop has Intel(R) Pentium(R) M processor 1.50GHz, frequency 600.000 MHz, lacache 2048 KB
 and memory 756M

Do you use the Flash plugin? I'm using it quite a lot and I'm experiencing the same problems based on the still quite unstable Flash plugin.

yes, i got a flash player

There is a known memory leak problem in some versions of FireFox. I'm not sure if there were any updates to fix this, and I am not sure which version this problem mainly applies to. What you can try to do though is change the amount of RAM dedicated to FireFox. To do this, open FireFox, and in the address bar, type:

about:Config

Once the page loads, right click anywhere on the page and select:

New

Another option box will appear, and from there select:

Integer

This will cause a dialog box to appear. In the dialog box, type:

browser.cache.memory.capacity

Now click "OK." Another dialog box should appear, and in there type:

16384

Click "OK." once more. Now close FireFox completely and restart. This should set the RAM dedicated to FireFox at 16MB.

Hopefully, this will stop FireFox from using up so much memory in your computer. Again, I'm not sure if the problem you are experiencing is due to this, but it is worth a shot to see if this will fix the problem. Good Luck.