FF 38.0.1 Slow. Rolled back to 37.0.2 and full speed ahead!
Friend updated automatically to 38.0.1. Complained of very slow response to typing and mouse activity.
Logged in for "over the shoulder" support and confirmed slow activity.
After checking all extensions and addons for any updates, still not working properly. Starting FF in safemode cured it as a test.
Found previous version, 37.0.2 and reinstalled. Problem gone.
Some sort of problem with 38.0.1 or with addons compatibility with 38.0.1.
Now that I am looking at how the screen is working, my install of 38.0.1 is also really slow.
You can try to disable hardware acceleration in Firefox.
- Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"
You need to close and restart Firefox after toggling this setting.
If you try Firefox Safe Mode, it will disable hardware acceleration and add ons temporarily and you can see if these are contributing to the issue. If it was indeed hardware acceleration see the update below.
Just as an update, after investigation of general hardware acceleration issues there is an update going out today that should resolve this. The new version will be 38.0.5 beta on June 2nd*. Thank you for your patience, please do report back if there are any further issues.
(*please note the update in this post for the change in release channel also subject to change)