Development Blog

Firebug 1.4 Activation

Firebug users like to mix debugging with web browsing. Since debugging can take up lots of machine resources, Firebug  supports ways for users to control the amount of resource and when that resource is used. In Firebug 1.4 there are two mechanisms:

  1. Web pages can be active or inactive.
  2. The panels Console, Script and Net can each be disabled or enabled.

We’ll just look at the activation part here. See Honza’s post for more info and the panel enablement.

Firebug maintains a whitelist and a blacklist of activation URIs.

  • greybug When you open Firebug, the selected Firefox tab has its activation URI is added to the whitelist.
  • 1.4.0-window-controls When you push the Firebug Off button,¬† the selected Firefox tab has its activation URI added to the blacklist.

The mapping of web page URI to activation URI is controlled with the option Activate Same Origin URL:


If you have Activate Same Origin URL checked (ON, the default), then the activation URI is created by taking the top two level of domain from the host portion of the the web page URI’s prepath. For example, would have an activation URI of

If you have Activate Same Origin URL unchecked (OFF), then the activation URI is the web page URI. In this case, Firebug also looks at links you click: if they have the same host as an active page, the resulting page will be placed on the whitelist and thus becomes active.

User commands (On) is stronger than Blacklist; Blacklist is stronger than Whitelist.

The lists are implemented as page annotations named firebug/history; the black list has annotation firebugged.closed; the whitelist has annotation firebugged.showFirebug.


Please post followups to the newsgroup.

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