mozconfig file: should bie -enable-default-toolkit='cairo-gtk2' - don't accepted only gtk2. Read about new Firefox features and ways to stay safe online. (I compiled it with gcc5 without further problems).Д®dit: A little correction for the attached. It seems it's definite not gstreamer causes this. I don't like pulseaudio, but may a try worth? (Only for the recent version ?). OPTIMIZED_FLAGS are OFF and the patch-memory-jemalloc-Makefile.in turned other optimations off. In Safe Mode, extensions and themes are disabled, so if you notice a significant improvement, you. If you want to test more points around the element for visibilityie, to make sure the element isnt covered by more than, say, 50it wouldnt take much to adjust the last part of the answer. Audio option is ALSAalso compiled with standard options. www/firefoxand www/libxulcompiled with standard options except OPTIMIZEDCFLAGSdisabled (caused problems in the past). For older Firefox support, check this answers history. Firefox-40.03,1 uses over 100 of one CPU, reaches up to 200 when I am playing videos (HTML5 not Flash, normal mode, not zoomed). To determine if an extension or theme is causing Firefox to use too many resources, start Firefox in its Safe Mode and observe its memory and CPU usage. Its supported in all major browsers, Firefox 9.0 being the last of them to add it. mozconfig file, cause to prevent the example files in the net and on the mozilla site.Д«ut this could not be the reason for the CPU usage of the current version of firefox. Extensions and themes can cause Firefox to use more system resources than it normally would.

This causes the segfault ( alsa segfaulted with jemalloc). mozconfig was -enable-optimized and some other optimizing flags.

Had also a problem with this version playing videos - freezes firefox and segfaulted. It plays the videos with normal CPU usage.

High cpu firefox 40.0.3