Like Mozilla Firefox, much of the genius in Mozilla Thunderbird is in its extensibility. While the wide range of excellent extensions for Firefox usually receive all of the attention, Thunderbird has many excellent extensions to bring additional features to the email client. The extensions that you will find most useful depend largely on your needs but, in honor of Thunderbird 2 being released (see my review in this post), here are some of the more useful ones.
Allow HTML Temp
‘Allow HTML Temp’ provides the ability to have HTML temporarily enabled in a selected message with one click. When moving to the next message, Thunderbird will switch back to the default mode. (Author’s Site) (Thunderbird Add-ons)
‘Contact Sidebar’ adds the address book to a quick access side panel allowing you to dock your address book for quick access and to easily add messages recipients. Note: If you are running Thunderbird 2 get a compatible version here. (Author’s Site) (Thunderbird Add-ons)
‘GMailUI’ adds Gmail like capabilities to Thunderbird. For example, an “Expression” search type that lets you enter multiple Gmail like operators into the search field at once or you can use the Gmail shortcut keys to navigate and file your email in Thunderbird. (Author’s Site) (Thunderbird Add-ons)
‘Lightning’ is an extension for Thunderbird that integrates Mozilla’s Sunbird calendar with Thunderbird and which allows it to perform email related calendaring tasks. (Author’s Site)
MR Teck Locak Install
‘MR Teck Locak Install’ provides numerous useful tweaks to Thunderbird. More for the advanced user. MR Tech Local Install will allow you to install extensions to Thunderbird that have not had their ‘maxversion’ number updated. (Author’s Site) (Thunderbird Add-ons)
‘NestedQuote Remover’ cleans up emails replies by deleting the deep nested quotes that are often part of long email threads. The extension can be set to automatically remove nested quotes which are deeper than a user-defined level or it can be manually activated via the context menu. (Author’s Site) (Thunderbird Add-ons)
‘Signature Switch’ offers removal and or insertion of a email signature with just one click of a button. You can define different signatures and easily select them via toolbar as well as providing automatic switching based on recipients. (Author’s Site) (Thunderbird Add-ons)
1. To be on the safe side before you install any of these extensions please backup your Thunderbird profile.
2. For most extensions listed below there is an author link and Mozilla Add-ons link listed. The version of the extension available at both sites may not be the same. The difference bring that the version at Mozilla Add-ons link has been tested and approved by Mozilla and is available directly from the Mozilla Update. Thus you can usually find the latest stable version of an extension on the author’s site before it appears on the Mozilla site as the whole testing and approval process takes time.
Update: Kyle Eslick has posted a similar list here that includes a few different extensions.