Two Types of Scripts
In an add-on's main scripts you can't do that, because the add-on code does not execute in the context of a page, and the DOM is therefore not available. If you need to access the DOM of a particular page, you need to use a content script.
This is the place where the main logic of your add-on is implemented.
Your add-on is implemented as a collection of one or more
CommonJS modules. Each module
is supplied as a script stored under the
lib directory under your add-on's
Minimally you'll have a single module implemented by a script called
"main.js", but you can include additional modules in
lib, and import them
require() function. To learn how to implement and import your own
modules, see the tutorial on
Implementing Reusable Modules.
While your add-on will always have a "main.js" module, you will only need
to write content scripts if your add-on needs to manipulate web content.
Content scripts are injected into web pages using APIs defined by some of the
SDK's modules such as
Content scripts may be supplied as literal strings or maintained in separate
files and referenced by filename. If they are stored in separate files you
should store them under the
data directory under your add-on's root.
To learn all about content scripts read the Working with Content Scripts guide.
API Access for Add-on Code and Content Scripts
The table below summarizes the APIs that are available to each type of script.
JSON. See the
reference at MDN.
require() is available, then so are the modules supplied in the
|The console global supplied by the SDK.
|Globals defined by the
self global, used for communicating between content
scripts and add-on code. See the guide to
communicating with content scripts
for more details.