High CPU use on new tab

I’ve had Activity Stream enabled for quite some time on my browser (Beta channel). Just today I realized that when I opened a new tab, then watched the two Firefox processes, they combined to use around 50-75% CPU while doing nothing. If I loaded a webpage then let the browser sit, CPU use drops to near zero.

I disabled Activity Stream and this behaviour wasn’t present any more. I re-enabled Activity Stream, and the problem seems to have gone away.

Definitely not of “bug report” caliber, but maybe a point of interest for someone. Maybe it’s happening to other people and they’re not realizing it.

Running OS X 10.11.6 and Firefox 55.0b1


Thank you for posting this, I am seeing the same thing although I initially thought it was to do with e10s. I toggled the Multi-process option in about:preferances and after a couple of browser restarts everything seemed to be fine. Having read what you have written, I have disabled Activity Stream and CPU utilisation is much calmer from the start (and with a bit less fan noise!).

Running TeaLinuxOS 8 and Nightly 56.0a1.

Filed a report over on their issue tracker: https://github.com/mozilla/activity-stream/issues/2732