Error in tracking tag: document.querySelectorAll is not a function

After installing the new version (0.4) and the new tracking tag, Firebug gives always an error when loading my page (

document.querySelectorAll is not a function, Line 8

Same problem occurs on

document.querySelectorAll is not a function, Line 8

What does that mean?

download the latest piwik.js from svn. There’s a bug in Firefox causing Firebug to log a dubious error message when various other firefox extensions are loaded (eg WebDeveloper).

If you still get the error after updating, file a bug with the Moz crew.

We don’t use querySelectorAll in piwik.js, so it would be a bug in FF3.5 and/or Firebug.

I didn’t download the last version of piwik.js but I disabled the webdeveloper extension: i have no more this error. For me is it now OK.
Thank you for the hint.