826331 - `hideChromeForLocation` is error prone for restartless add-on

Status: NEW

(Firefox :: Tabbed Browser, defect)

Description

[Matteo Ferretti [:zer0] [:matteo]]

The code suggested in bug 628863 and on MDN (https://developer.mozilla.org/en-US/docs/Hiding_browser_chrome) is error prone on restartless Add-on.

If a restartless add-on is chaining the `hideChromeForLocation` method as suggested in the MDN:

    XULBrowserWindow.hideChromeForLocation = function(aLocation) {
      return (/* your test goes here */) || prevFunc.apply(XULBrowserWindow, [aLocation]);
    }

When is unistalled or disabled, it will probably set the `prevFunc` back to the `hideChromeForLocation` method. But let's say that add-on A and B are chaining both this method: if add-on B is disabled, then what's happened to the function chained previously by add-on A?

We should provide a safer approach to the add-on developer.
For example, `inContentWhitelist` could accept not only string, but regexp and function as well, and be more flexible. In this way, an add-on will just remove its function (or regexp) from the list during the cleanup; without affects any other add-on.