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    Firefox 23 for developers

    Changes for Web developers

    Security

    • Mixed content blocking. Firefox will no longer load non-secure (http) resources on secure (https) pages (bug 834836).
    • The standard syntax of CSP 1.0 policies are now implemented and enforced by default.

    Developer Tools

    • A Network Panel has been added to the developer tools. This is more detailed view than the "Net" view option in the Web Console.
    • Web Console has been renamed "Console", and includes the option to filter security errors/warnings.
    • The new Toolbox Options lets you disable features, change light/dark theme, or enable Chrome/Remote debugging.

    HTML

    JavaScript

    • The Object.defineProperty method can now be used to redefine the length property of an Array object.
    • The option to disable JavaScript, including the options to allow moving windows/replace context menu, have been removed. You may still disable JavaScript by double clicking the "javascript.enabled" option in about:config.

    DOM

    CSS

    • The blink effect for text-decoration: blink; has no more effect, but is still a valid value (bug 857820).
    • In-flow ::after and ::before pseudo-elements are now flex items (bug 867454).
    • The way to compute viewport units has been changed. In conjunction with overflow:auto, space taken by eventual scrollbars is not substracted from the viewport, whereas in the case of overflow:scroll, it is. (bug 811403)

    MathML

    • Negative widths for the <mspace> element has been implemented (bug 717546).
    • The <semantics> element now determines the visible child as described in the MathML3 specification.

    Changes for addon and Mozilla developers

    Firefox developer tools

    Addons that overlay chrome://browser/content/debugger.xul must now overlay chrome://browser/content/devtools/debugger.xul. You may add references to both these files in chrome.manifest for compatibility.

    See also

    Older versions

    Document Tags and Contributors

    Last updated by: teoli,