Firefox - enable reporting of Javascript errors

Question

How do I make Firefox pop up something on every Javascript error? I don't want to use add-ons for this basic functionality, I don't need fancy debugging or anything, just to immediately see if there's a Javascript error and on which line it is.

I tried about:config and setting devtools.errorconsole.enabled to true, but it still won't report errors (IE and Opera do).

Answer 1

Firefox uses the error console to present the errors found on a web page.

To see it, press ctrl + shift + j.

Other browsers like Microsoft Internet Explorer have opted to alert the errors found by default, that is why you see them on an popup.

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As can be read on the MDN Error Console page:

The Error Console is a tool available in most Mozilla-based applications that is used for reporting errors in the application chrome and in web pages user opens. It reports JavaScript-related errors and warnings, CSS errors and arbitrary messages from chrome code. In Firefox, the Error Console can be opened from the tools menu or by Ctrl-Shift-J.

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For an immediately presentation of errors on Firefox, for anyone willing to use add-ons:

Console² has an option to gain focus automatically when errors are found.

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Web Developer contains three icons, one for DocType, other for CSS and other for JS errors, allowing you to know whenever an error occurs.