How to Change the Default Browser in Thunderbird

It's convenient having your inbox, sent box, and other mailboxes with you no matter where you go, just by logging into popular services like Gmail and Yahoo! Mail. But whether for privacy and security concerns or technical ones, there are many reasons to use a desktop-based email client. Among the open-source choices, Mozilla Thunderbird is one of the most popular. While this software is generally user-friendly, configurable, and easy to work with, there are occasional bugs and interface decisions that make for a bumpy ride.

These instructions apply to Thunderbird 11.0.1 through 17.0.8. Results in other versions may vary.

The Problem

Thunderbird doesn't operate alone. When you install Thunderbird on your computer, you're installing it with a number of other applications. Some of these applications may get called into action based on the contents of your emails. In the case of the uniform resource locators (URLs) you click, like website addresses, Thunderbird usually passes the event off to your default web browser.

Under normal circumstances, this all goes off without a hitch. Most operating systems give you the option to choose a default web browser in some configuration screen, and most web browsers give you a way to choose them as your default option. Sometimes, however, things go wrong, and you need to know how to tell Thunderbird explicitly which web browser you want it to use.

Set the Default Browser in Thunderbird

This technique does not change your default web browser across all of your applications. This setting affects Thunderbird only.

On Linux, this change should work on your particular distribution with your particular desktop environment. If you want to create symbolic links to your web browser under an alias, edit /etc/alternatives/, or dive into the Thunderbird Config Editor, the following suggestion is just as likely to work and will save time.

Open Thunderbird.
Go to the Edit menu and choose Preferences.
In the Preferences window, select the Advanced tab.
In the lower-right corner of the window, select Config Editor.
Another window will open, warning you that you can potentially break Thunderbird in the Config Editor. Select I accept the risk to move forward.
Use the search at the top of the Config Editor window to look for network.protocol-handler.warn-external.http.
Double-click network.protocol-handler.warn-external.http and network.protocol-handler.warn-external.https to set their value to True.
Close the Config Editor.
In the Preferences window, select the Attachments tab.
Go to the Content Type column and look for http (http). Select the value in the Action column in the same row to see a list of choices that includes the web browsers currently installed on your computer. Choose the new action you'd like Thunderbird to take when it encounters a URL that starts with http.
Do the same for https (https) in the Content Type column. This will cover every time Thunderbird opens a URL that begins with https.
Press Close to exit the Preferences window.
Restart Thunderbird.

If everything worked, Thunderbird will send clicks on URLs to whatever browser you selected.

Pro Tip

By following the steps above, you can set Thunderbird to use a web browser other than the default one the rest of your computer's applications use. This could be handy if you're concerned about viruses coming in through emails, and you only want to view these web pages in a high-security web browser.

And, you can handle HTTP-based URLs with one browser and https-based ones with another. Again, this could be something to consider for both security and privacy issues. While you may trust your https (encrypted) requests to any of your installed web browsers, you may want your HTTP (non-encrypted) requests handled by a different browser.