Prefer .isInstance() in chrome scripts over the standard instanceof operator for DOM interfaces, since the latter will return false when the object is created from a different context.

These files are covered:

  • *.sys.mjs

  • *.jsm

  • *.xhtml with

  • *.js with a heuristic

Since there is no straightforward way to detect chrome scripts, currently the linter assumes that any script including the following words are chrome privileged. This of course may not be sufficient and is open for change:

  • ChromeUtils, but not SpecialPowers.ChromeUtils

  • BrowserTestUtils, PlacesUtils

  • document.createXULElement

  • loader.lazyRequireGetter

  •, but not

Examples of incorrect code for this rule:

node instanceof Node
text instanceof win.Text
target instanceof this.contentWindow.HTMLAudioElement

Examples of correct code for this rule: