Firefox/Feature Brainstorming:Add-ons

Add-on management

Version compatibility
Options management
Integration with AMO
Make extensions "cleanware". Let all of their configuration lie in their own file directory instead of mashing it together with other extensions' configuration in One Big File. This reeks of Windows' "Registry Hell". Cleanly uninstalling an extension should be as simple as deleting its subdirectory.
Extensions should have compatibility mode to allow older extensions to run when a new revision of firefox is released and extension is not available. Maybe offer a "force install" to see if an out of revision extension will work.
- See Nightly Tester Tools extension that is able to force such install mode over any given extension (or at least over most of them).
Should be able to view date and time that extension was added, and sort extensions by that date (to aid debugging, by removing extensions in reverse order, until a recently-seen problem ceases to exist). Andy Mabbett

"Update All" extensions button
Provide changelogs for extension updates (Do I really want to update?)
When the plugin finder doesn't find any suitable plugin, show a description for making easier to the user to find it (show data type?)
«Visit Home Page» opens extension's home page in a new window; must have another context menu item to open it in a new tab.
Allow us to specify which order each plugin will sit in.
Add a option to install plugin for Single User or All User mode while installing the XPI via the GUI.
Swap any special feature to an extension and add an Extension Manager that works like the Eclipse Callisto Project, so Firefox would be lightweight and functional
Ability to group extensions and themes into folders that can be enabled, disabled, and uninstalled as a group

Support for remote extensions (i.e. dev tools package)
Store XPI files in a central location so multiple users on the same machine do not have to download the same XPI multiple times. Maybe allow user to set location so only one download is needed for multiple users on a corporate network.

Allow user to disable plugins via "about:plugins", Options/Prefs, or Extensions
Dynamic loading/unloading of extensions. No more restarting just because an extension was installed/uninstalled/updated. (Like nglayout.debug.disable_xul_cache = true, only better.)

Have "Extension Packs" available for download immediately upon completing a Firefox install (also see "Installer" notes)

Limit amount of Plugins/Addons from overwhelming the Interface. Allow Firefox to limit 2-20 lines of toolbars for real estate recovery. Have Arrow Up and Arrow Down at the start of the Toolbar rotator or use the scroll wheel (when mouseover the Plugin toolbar) to rotate between plugins.

Flash plugin to let the Windows version of Flash run using Wine (or similar.)
- Since the Linux version will always be several versions behind what is used on most web sites and honestly expecting this to change is bordering on insanity, provide a way to run the Windows version under Firefox.
Fix the Flash Installation on Linux
- One always winds up having to do a manual install. If Firefox needs root permissions to do the install ask for the root password, don't just fail out.

Allow plug-ins to add support for file formats not supported by gecko (in ex. PDF, iCalendar, MS .doc files) or supported but needed to render differently (in ex. XHTML, feed RSS, IE rendering support)

Improve extension installation/management UI
Unify add-ons management (extensions, themes, search engines, dictionaries, plugins)
Improve interaction design around customizing browser interfaces

Have an option for a theme to use svg images for icons so that users can adjust icon sizes. As it is now, I must provide 3 themes (e.g. -SphereGnome, SphereGnome_Big and SphereGnome_Jumbo) to present 4 icon sizes from 24x24-pixel to 64x64-pixel images.
Have an option to use variable system icons. For example, my themes use 16px, 24px and 32px images for menuitem images, tab favicons, etc.

Have an option for a user to choose background images supplied by a theme. Currently, I have four themes set up essentially to deliver different backgrounds. With variable icon sizes and switchable background images I could reduce my SphereGnome-based themes to two, and my Scribblies themes to one.
Have an option for a user to choose no background image. A number of users request "plain" themes.