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Plugins versus Extensions

An attempt to cut through the confusion created by Mozilla developers

Copyright © 2017, 2021 by David E. Ross

An important feature of several different browsers is the ability to add extensions to modify or add capabilities. Beyond extensions, plugins can add capabilities not only to browsers but also to other applications.

Two unfortunate decisions were made by the developers of Mozilla-based applications with respect to both plugins and extensions:

• The Mozilla developers decided to lump plugins and extensions together under the same term "add-ons". This sowed confusion among users of Mozilla-based applications, confusion that could be never ending.
• However, the confusion might indeed end because the Mozilla developers then decided to eliminate the capability to have plugins and to change significantly the interface that allows extensions.

To make sense of all this, users need to understand the differences between plugins and extensions. The differences are indeed major.

Plugins

A plugin is a software application that can be used by another application.

• A plugin is installed by the computer's operating system (e.g., Windows, Linux, macOS).
• A single plugin, once it is installed, is available to all other applications that contain the appropriate interface to use it.
• A plugin cannot be uninstalled for only one application but remain available to other applications. It exists for all applications or for none.

On my PC, the same plugin (doPDf) to "print" to a PDF file is available to my browser (SeaMonkey), my E-mail client (Thunderbird), Word, Excel, GIMP (GNU Image Manipulation Program), and others. It is even available to Adobe Reader, where I use it to strip away locks that prevent modifications. I installed doPDF only once to make it available to all. However, it actually installed as a plugin to my PC's print server. I could have enabled its plugin for Word and Excel, but I disabled that.

For SeaMonkey, I have enabled one plugins, an old version of Flash — a version prior to the ones that self-destructed — needed by one Web-based game I sometimes play. I have no plugins enabled for Thunderbird.

Note that, while the Mozilla browser Firefox now blocks plugins, plugins will still be available for non-Mozilla applications.

Extensions

An extension can be perceived as a software fragment for a single application.

• An extension is installed by the application that is to use it.
• When installed, an extension actually changes the internal software of the application. This change is done in a manner that allows the extension to be disabled or even uninstalled.
• Some extensions can be used by more than one application. For that to happen, it must be installed separately for each application.
• Thus, an extension can be uninstalled for one application without affecting the fact that it was also installed for another application.
• For older Mozilla applications, extensions are files with the .xpi file-extension. These files are actually zipped files that can be opened with such applications as Winzip and 7Zip.

On my PC, I have 26 extensions installed for SeaMonkey:

• Four extensions restore old capabilities that the developers decided users no longer needed. Collectively, users downloaded 12,198 of these four, saying the developers were wrong.
• One extension implements an internal capability for SeaMonkey that already exists in Firefox to replace the need for a plugin.
• Two extensions implement capabilities that the developers assert users do not need. Collectively, users downloaded 12,811 of these, disputing the developers.
• Two extensions implement capabilities that the developers indicate might be made internal to Mozilla-based applications some undetermined time in the future.
• The remaining 17 extensions enhance my ability to use SeaMonkey.

Also on my PC, I have 12 extensions installed for Thunderbird. These can be characterized similarly to those for SeaMonkey. Indeed, four of them are the same as those I installed for SeaMonkey. When new versions of those four are released, I must install them twice, once each for SeaMonkey and Thunderbird.

The Future for Mozilla

Plugins are already blocked in Firefox, and this change is expected to propagate soon to SeaMonkey and Thunderbird. Additionally, the interface for extensions will block those that have the .xpi file-extension. Following a trend to make Mozilla-based applications more like Google's Chrome, Firefox will only accept Webextensions; this change too is expected to propagate soon to SeaMonkey and Thunderbird. I see two major problems with this change to the extension interface:

• Extensions are developed by individuals outside of the Mozilla organization. While some of those individuals no longer maintain their extensions, the extensions themselves still work quite well. Mozilla is not putting any effort into converting .xpi extensions into Webextensions. Thus, capabilities desired by end-users will be lost.
• The more Mozilla developers make their applications more like Chrome, the more end-users will abandon Mozilla-based applications. After all, why use a mimic of Chrome when the real thing is available for free?

I continued to use Eudora Lite as my E-mail client long after Qualcomm stopped maintaining it. I changed to Thunderbird only after Eudora Lite would not interface with the E-mail server of a new ISP to which I was forced to change; soon thereafter, Eudora Lite would install in a newer version of Windows. I plan to use the last versions of not Chrome-like SeaMonkey and Thunderbird as long as they remain functional and can be installed.

7 July 2017
Updated 21 December 2021

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