I have been using kubuntu quantal and for some time I have been experiencing terrible performance issues with gtk apps. Especiall in Mozilla Thunderbird I need to wait a few seconds before a letter appears while typing. But also firefox and IntelliJ Idea work slowly. It seems to have started when I have upgraded RAM from 6 GB to 12 GB. Is it at all possible that by doubling the RAM memory the system got slower?! If not, what can it be ? Or at least how to diagnose it at all?

I have HP Elitebook 12 GB RAM, AMD Radeon HD 6470M (tried using the mesa and fglrx drivers provided by Ubuntu, will try also the upstream drivers by AMD), intel core i5, so it is definetely not an issue of poor hardware.

Thanks in advance for any help.