Hey there, I love Google's little Page Speed tool, I've seen some wonderful speed advances on sites I've worked on because of it, but since I've upgraded to FF4 it doesn't seem to be in Firebug anymore. And when I've tried to download it, it won't install.

Is it just me, or are Google being slow to update it? (Seems odd.)

Here's where I've checked: http://code.google.com/speed/page-speed/

2 Answers 2


If an extension does not have official support for Firefox 4, you can choose to bypass the version checking in Firefox:

  1. In the address bar enter about:config (read & accept any warnings to proceed)
  2. Right-click and select New > Boolean from the menu
  3. Enter extensions.checkCompatibility.4 for the preference name
  4. Enter false for the preference value

Firefox should now allow you install extensions which aren't explicitly compatible with v4.*, although you might need to restart Firefox for the setting to take effect.

If you had the extension installed when you upgraded to 4, you probably still have it installed: you can check in about:addons.

Once the compatibility check is disabled, you should be able to enable any previously blocked extensions.

  • Bah, dont use those links. Looks like SE coerces them into HTTP; type them literally into your browser instead. May 7, 2011 at 4:10
  • +1 for clear, concise answer; edited to correct FF settings links
    – danlefree
    May 7, 2011 at 5:56
  • Thanks for that. Good to know, but probably not a great idea. I'm guessing there's a reason say the current version isn't compatible. May 7, 2011 at 23:03
  • @Django - not necessarily, FF4 is only new so the most likely reason is that the maintainers simply haven't got around to updating it. May 8, 2011 at 5:19

You didn't mention which specific version you were working with, but there was a release candidate posted to the PageSpeed Google Group last week that seems specifically targeted at v4. (Current version is 1.10, that RC is for 1.11.x)
Might be better than hacking the compatibility value and hoping the UI changes don't blow anything up too badly.

  • Excellent. Seems to work OK. I hope it auto-updates when the new version goes live! May 7, 2011 at 23:01

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