August 03, 2005

OSCON: Supercharging Firefox with Extensions

Extensions are code that run in the browser just as if it was a part of Firefox. This talk is geared around "the trunk" (the upcoming Firefox 1.5). Popular examples:
  • AdBlock
  • Greasemonkey
  • BugMeNot
  • FoxyTunes
  • Many toolbars: Google, Yahoo, A9, Netcraft
Structure of an Extension
  • Install Manifest -- structure of extension, and where it should go in the Firefox system. Aids in deinstallation. No protection -- extensions can be written that don't cleanly uninstall.
  • "Chrome" (User Interface components)
  • Components (non-UI) - integrate with services, hook to other parts of system, etc.
  • Defaults (Preferences)
Packaging
  • "Zippy" files: zip file with a .xpi extension.
  • Can package traditional "heavyweight" plugins (flash, pdf reader, etc.) as Zippy files
  • Don't need GUID's anymore for directory name for extension.
  • install.rdf file needs to be in root of .xpi.
UI Development with XUL
  • Long topic; good resources for XUL development at developer.mozilla.org.
  • Supplies UI controls, drag-n-drop, menus, toolbars, etc.
  • Bound to actions through JavaScript
  • You can do overlays, over Mozilla-supplied XUL, to plugin your own UI elements for the extension. XUL overlay can add, remove, or change elements in existing XUL.
  • XUL is a document, which can be manipulated just like you would a DOM in DHTML.
  • Site: xulplanet.com
Extension bits:
  • Chrome Manifest -- where to put overlay and where to find it.
  • Install Manifest
    • RDF/XML file
    • Identifies extension
    • Compatibility extension (allows to install in Thunderbird and Firefox, for example)
    • Take existing file and modify it -- to hard to do from scratch. Or grab an RDF generator.
    • Update information -- for update checking
    • Save as install.rdf
New testing bits:
  • Can point firefox at a directory, so you don't need to repackage.
  • Still need to restart browser to have it pick up new extension. But it seems like the browser will pick up code changes dynamically?
  • If you turn off XUL cache, may not need to restart Firefox.
Creating New UI:
  • Dialogs are in separate .xul files
  • Functionality in .js files
  • Use DOM methods to manipulate UI elements within XUL
  • Use .css files to add images, set colors, change style, etc.
XPCOM Components
  • Firefox supports XPCOM components in extensions
  • This allows implementing code in JavaScript, C++ (Gecko SDK), etc. -- interacts with more of "the guts" of Firefox.
  • Automatically registered by putting these files in components/ directory.
Posted by andyr at August 3, 2005 05:09 PM
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