I recently bought a new Acer Aspire 5. It seems to have very similar specs to an Asus I previously owned, ie Intel Core i3 and 4GB of DDR4 memory. But unlike the Asus, it has serious performance issues. I'm now on 18.04. I never ran the Asus on anything higher than 16.04. My problem now is that as soon as I open about 10 tabs in any browser (tried Chrome, FF and Vivaldi), the whole system starts lagging badly. And sometimes, even when I have only a few tabs open, and I try to switch between applications with alt-tab, there is an extreme delay of several seconds before anything happens. I already changed to Xfce from Gnome, but that didn't help much. What else can I do and how can I find the reason for these problems?