Comment 35 for bug 548866

Yes, if you read the full text of the changelog, it contains:
  * Prevent LP: #643899 - Firefox sending header "Accept-Language:
    chrome://global/locale/intl.properties" because the intl.accept_languages
    preference is messed up. Drop a patch which causes the preferences
    system to save a user preference when changing a preference value to equal
    the system default value (and revert to the original behaviour where the
    preference is just discarded). This should hopefully stop Firefox Sync
    from breaking localized preferences where they haven't been modified by
    the user, but does regress LP: #548866

which has been parsed as closing #548866.