This may be caused by a specific extension.

To diagnose performance hogs caused by specific extensions, restart Thunderbird with add-ons disabled (Thunderbird Safe Mode).

On the Help menu, click on Restart with Add-ons Disabled. If Thunderbird works normally, there is an Add-on or Theme interfering with normal operations.

You will need to re-enable add-ons one at a time until you locate the offender.

Thank you for your reply.

Starting Thunderbird in Safe Mode does change the Activity Monitor status so that it reports that the High Performance GPU is no longer required.

Unfortunately when not in Safe Mode, but with all Add-ons (Plug-ins and Extensions) disabled the Activity Monitor again reports that the High Performance GPU is required - suggesting that it is a problem with the configuration of Thunderbird itself.

(I'm using the Default 31.0 theme.)

Have a look at this link: https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

under 'Steps' heading there is quite a list of things to check.

Thank you. I've been through the steps, my memory usage appears to be quite normal. There was a suggestion to try a beta version but the only betas I can find are all older than the current version I have.

I also run Firefox 31.0 (with similar add-ons) and that does not exhibit the GPU problem at all.

The bug appears to be raised here: https://bugzilla.mozilla.org/show_bug.cgi?id=689742 . It starts life as an issue on OS X and turns into a fix for Windows. If it is the issue I'm seeing It doesn't fix OS X.

I think I may have the solution.

The bug report here: https://bugzilla.mozilla.org/show_bug.cgi?id=693852 says in its last comment (8) that the "Hardware acceleration has now been disabled by default for TB 9".

It isn't disabled by default anymore.

However if I use the Config Editor to 'set layers.acceleration.disabled preference to "true"', as suggested in the first comment on bug 693852, the High Perf GPU problem goes away.

I was just going through a load of bug reports when you found the answer ahead of me. Many thanks for the excellent reporting and feedback. I'm sure this could be of assistance to others.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

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