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Firefox 38.0.5 consumes a lot of CPU on OS X 10.10.2 (Macbook Pro)

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I've updated to the latest Firefox (38.0.5) and found the performance of my computer to be really really slow (it is a pretty beefy MacBook Pro with an i7 and 16GB memory).

I saw that the CPU usage was really high, and the computer was getting really hot.

I've since then updated my add-ons and plugins (mainly Java and Flash), and the problem persisted.

I restarted Firefox in Safe Mode, and the CPU usage was still really high.

I did not have this problem on a previous version (not sure when this issue exactly started, i.e. whether it was 38.0.5 vs 38.0.1, but it's been fairly recent)

I saw a bug report about high cpu usage, which said that the potential issue was fixed on 38.0.5, but obviously some problem persists.

Thanks, Sridhar

All Replies (3)

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Hi,

Thanks for your reply. https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix was the very first site I checked to try to resolve the issue.

I made sure my firefox was the latest version (it was - I suspect the problem may be here?). I also updated all my plugins. I also started Firefox in Safe Mode, but the high CPU usage persists.

The only thing I didn't try was to stop scripts and intrusive content, using a plugin such as NoScript

Once I had NoScript running, CPU usage went down drastically. The interesting thing is that these I've had tabs open for a bunch of websites forever, and the excessive CPU usage is only now showing up, so it seems that intrusive content that's eating up CPU seems hard to explain.

Perhaps some change in 38.0.5 is very sensitive to scripts and their processing?

Anyway, I'll try to narrow down which page(s) are the culprit (or at least contributors), and will update this thread.

Thanks, Sridhar

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Ok, I enabled all scripts on NoScript and restarted Firefox, and after an initial burst of high CPU, it settled down.

So it looked like some script on some page started to consume a lot of CPU, but has since been fixed?

It will be nice if we can get cpu information for individual tabs/windows to help isolate the problem page.

-Sridhar