These three panels (Console, Script, Net) have the potential to incur a great deal of overhead into any web sites that utilizes them. There are two pain points, in particular: The Mozilla JavaScript debugger and network monitoring. The Mozilla JavaScript debugger is used in two ways in Firebug: First it is used in the Script panel (to debug JavaScript code, naturally), second it is used to figure out where JavaScript errors are coming from in the console. Network monitoring is, naturally, used for the Net panel. Here’s the important point: The Mozilla JavaScript debugger and network monitoring are both global to Firefox not localized to a single window or tab. This means that when you enable a panel, such as the script panel, it will turn on the JavaScript debugger for all JavaScript code in Firefox. Rob Campbell has run some initial numbers and has found that, simply, enabling the script panel anywhere in the browser immediately slows down all JavaScript execution by 25% – for all JavaScript on all tabs in the browser.

We don’t have solid numbers on the networking monitoring overhead yet but we imagine it to be much less, although still occurring on a global all-tabs scale which isn’t desirable. The important question here is: What is being done to stop this?įirst, it must become necessary to not incur any overhead when using the console panel.

This is a ubiquitous part of Firebug and any global overhead presented by it must be removed.

This can be done but not without some internal API changes to how Firefox handles and reports error messages. We hope to have something introduced in an upcoming version of Firefox so that we can compensate appropriately in Firebug. Second, the JavaScript debugger must be improved. A number of bugs have been filed on this subject and we hope that some of them will make their way into upcoming versions of Firefox (Firebug will be able to immediately improve when that happens).

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