When I have about 15 tabs open, Firefox uses processor cycles continuously. Concretely, usage is about 10% on my new Inspiron 11 3000 with a quad-core Pentium. The effect persists even when Firefox runs in safe mode and when none of the open sites have advertisement. It also persists when the NoScript plugin is in use to prevent execution of extraneous JavaScript. Minimizing all windows appears to alleviate the problem substantially, though I don't like to do this because it causes thumbnail representations of the windows to be lost. Note that my environment is Firefox v32 running under Ubuntu 14.04, as seen in the automatically provided troubleshooting information. What might explain the effect described above, and how can I achieve the more acceptable level of demand for processor power observed when windows are minimized, without actually minimizing all windows?