Font settings in Thunderbird

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This article was written for Thunderbird 1.5. For earlier versions, the menu sequences described below may differ.

This article provides an overview of the various font/character settings in Thunderbird, which are often a source of confusion for new users. Broadly speaking, font settings can apply to three things in Thunderbird—message display (and composition), message sending, and the Thunderbird user-interface—and the settings for each are controlled separately. Please ask for help with font-related issues in the MozillaZine forums.

Basic terminology

Key concepts and terms related to font/character settings in Thunderbird:

  • Text format: plain text vs. HTML—see the overview in the plain text e-mail article. A message's text format is also known as its content type.
  • Character width: variable width (proportional) vs. fixed width (monospace)—in fixed width fonts, all characters are the same width. E.g., "i" and "l" are not narrower than "w" and "O", as they would be in a variable width font (visual examples). Traditionally, plain text messages are viewed in a fixed width font, but you can set Thunderbird to use a variable width font if you prefer. A font's character width is also known as its spacing.
  • Font style: serif vs. sans-serif—see these visual examples. Serif is the default variable width font style in Thunderbird, but you can change it to sans-serif if you prefer.
  • Character encoding—most likely you won't need to worry about this unless you send/receive plain text messages in more than one language. E.g., if you send a plain text message containing Japanese characters, you won't want to use a "Western" character encoding because the Japanese characters won't get sent properly. A message's character encoding is also known as its charset.

Message display

This refers to what messages look like when you view them or compose them. Changing the message display settings will not affect your outgoing messages in any way. For instance, if you set Thunderbird to display messages in Verdana font, size 24 (pixels), this does not mean that your outgoing messages will be sent in the same font and same size by default.

Settings via the Options/Preferences dialog

On Windows, these settings are accessed in Thunderbird via "Tools -> Options -> Display". Linux and Mac OS X users, see Menu differences in Windows, Linux, and Mac.

  • Text format ("Tools -> Options -> Display -> Formatting"): if you don't like viewing plain text messages using a fixed width font, this is where you can change it to use variable width instead.
  • Font and font size ("Tools -> Options -> Display -> Formatting -> Fonts..."):
    • Ensure that the "Fonts for" choice at the top of the dialog is set to the language group that you want to change. Thunderbird treats Unicode messages (for example, UTF-8) as being in the same language group as your system. (Thunderbird 3beta does not, so: For Unicode messages (UTF-8), set "Fonts for" to the language group named "Other languages". See bug 91190, #47.)
      • Thunderbird determines a message's language group from its charset (character encoding). Use menu "View -> Character Encoding" to uncover the language group and charset of an individual message. For example, you might receive some email encoded with western charset=ISO-8859-1, and some news feeds encoded with unicode charset=UTF-8.
    • Using the "Proportional" pulldown menu (screenshot), you can choose either "Serif" or "Sans-serif" as your default variable width font. Using the "Serif" and "Sans-serif" pulldown menus, you can choose the specific fonts (Times New Roman, Arial, etc.) that you want to use for each font style.
    • Font sizes are set separately for "Proportional" (variable width) and "Monospace" (fixed width) fonts.
    • Minimum font size: it's useful to choose a minimum font size if you sometimes receive HTML-formatted messages where the sender uses a font size that's too small on your monitor. Overly small text will be enlarged to your minimum font size so that you can read it more easily.
    • Language-specific font settings: in addition to your standard font settings, you can also adjust the font settings for other languages that you use. In the "Fonts for" pulldown menu, select the language you want to change (e.g., "Japanese"), and then make your font settings as desired. (Note that the "Minimum font size" setting for a language group sometimes appears to be set when it is really None. This is bug 364336. To work around it, close and reopen the dialog.)
    • "Allow messages to use other fonts": Normally leave this box checked to allow HTML messages containing font changes to display in the way the author intended. Clear this checkbox to force HTML messages to use your font choices in this dialog. This is a single setting that applies to all the language groups.
  • Character encodings ("Tools -> Options -> Display -> Formatting -> Fonts..."):
    • "Outoing Mail" pulldown menu: although this is listed in the "Display" dialog, it's actually not a message display setting. Instead, it applies to messages that you send (see the "Message sending" section below).
    • "Incoming Mail" pulldown menu: Thunderbird will normally use each message's stored character encoding, or auto-detect it, but you can set a default character encoding for message display by using this pulldown.
    • "Apply the default character encoding to all incoming messages": For normal use, do not check this box. It forces the selected character encoding on all messages, even if it is the wrong character encoding, making some messages unreadable.
    • "Use the default character encoding in replies": For normal use, do not check this box. It is sometimes useful if you often receive messages in one language but you reply in a different language, but it might mean that the person you reply to cannot read your reply.

Other message display settings

  • Font size (temporary): "View -> Text Size", then select "Increase" or "Decrease" to temporarily display the text in a larger or smaller size. This will reset to "Normal" the next time you start up Thunderbird. Keyboard shortcuts: hold down the "Ctrl" key and press "+" to increase the text size, "-" to decrease the text size, or "0" to reset it to normal.
  • Character encoding (temporary): "View -> Character encoding", then select " the desired character encoding.
  • HTML simplification: "View -> Message Body As -> Original HTML / Simple HTML / Plain Text". The "Simple HTML" choice displays messages without any HTML formatting except bold and italics. This can be useful when you receive a message with a layout, color or font size that makes it difficult to read.
  • Signature color: text below the signature separator ("-- ") is normally displayed in gray rather than black. Advanced users can set a different display color as described here.
  • Display names: "Show only display name for people in my address book" on the Options (Preferences) – Advanced – General tab, hides the address in message headers if the address is in your personal address book. The hidden address is placed in a tooltip, which pops up when you position your mouse pointer over the header.
  • For example, if the header is really Fred <> and if is in your personal address book, then you only see: Fred   The name that you see is the display name in the message, not the display name in your address book. (This is the subject of bug 243631.)

    This setting only affects the way Thunderbird displays individual messages. It does not affect columns in folders (the thread pane), and it does not affect From or Reply-To headers.

Advanced techniques

Advanced users can change the way Thunderbird displays messages by using a userContent.css file.

Advanced users can choose View -> Message Source to troubleshoot message display problems. To identify problems with outgoing messages, it is usually enough to save a test message as a draft, then select it in the Drafts folder and view its source.

Message composition

The message display settings in the above section also apply to messages that you compose. The settings are not sent, so they do not affect how your messages appear to recipients.

The settings in this section can affect how messages are sent. If you make unusual choices, then people who receive messages from you might find them difficult or impossible to read.

Setting your standard preferences

  • HTML or plain-text compose: which do you want to normally use when composing messages? If you normally want to compose in HTML, go to "Tools -> Account Settings -> [account name] Composition & Addressing" and check the box for "Compose messages in HTML format". This is an account-specific setting and thus must be set individually for each of your accounts.
  • HTML font preferences, for when you do compose messages in HTML mode: these settings are accessed via "Tools -> Options -> Composition -> General -> HTML Options". It is usually a bad idea to change these settings, because people who receive your messages might find the messages difficult to read.
    • Font: "Variable width" is default. Using "Variable width" actually doesn't do anything to the text in the message body; it just leaves the font style unspecified. Using "Fixed width" means that your message text will specifically be marked as fixed width (using <tt> tags).
    • Size: "Medium" is default, and using this actually just leaves the font size unspecified. This is the recommended setting, since recipients will then see your message text displayed according to the default font-size settings in their mail clients. Keep in mind that people do not all have their monitor resolutions set the same as yours, so that if you choose a larger or smaller font size because it looks "right" on your monitor, you can't be sure how it will look on the recipient's monitor.
    • Color: if you must.
See also: Default HTML font for new messages - Thunderbird
  • HTML send options (via "Tools -> Options -> Composition -> General -> Send Options..."): use the "Text Format" pulldown menu to tell Thunderbird how to handle your outgoing HTML-formatted messages. Keep in mind that even though you may normally compose in HTML mode, it doesn't mean you have to normally send your messages with HTML formatting.

Per-message settings

Things you can change when composing a message, to override your standard font preferences:

  • HTML/plain-text compose: hold down the "Shift" key and click on the "Write" button to compose a message in the mode that's not your default.
  • Fonts in HTML compose: in the Compose window, you can choose any font from the Formatting toolbar. As noted above, if you choose "Proportional" as the font for all or part of the message text, this will simply leave the font unspecified.
  • Other styles: Advanced HTML message style settings are available in the Compose window when the cursor is in the message body via "Format -> Page Colors and Background". You can specify text and link colors, and the page background, which can be an image. To add custom CSS styles, use the Advanced Edit... button. A bug in some versions means that these settings are not always cleared when you compose another message.

Message sending

Thunderbird sets a message's final format (HTML, plain text, or both) and its character encoding when you send the message. If you save the message as a draft, it sets the character encoding at that time, but the format might change when you send the message.


The default message format (HTML, plain text, or both) is set in "Tools -> Account Settings -> [account name] Composition & Addressing". This is an account-specific setting and thus must be set individually for each of your accounts.

The format can be overridden for a domain (the last part of an e-mail address, like according to the domain lists in "Tools -> Options -> Composition -> General -> Send Options". The format can also be overridden for an individual e-mail address in your address book.

You can specify the format on a per-message basis in the Compose window using "Options -> Format". This choice overrides all the other settings.

Holding down the SHIFT key when beginning a message (by clicking "Write", or "Reply" for example) sets the message format to HTML, even if "Compose Messages in HTML format" is disabled in the account settings.

Character encoding

Character encoding is only important for messages that are sent as plain text. HTML-only messages can include any characters at all, regardless of the character encoding.

The default character encoding is set in the message display settings in "Tools -> Options" -> Display -> Fonts". Use the "Outgoing Mail" pulldown menu to specify the default character encoding for messages you send.

You can specify the character encoding on a per-message basis, inside the Compose window via "Options -> Character Encoding".

If you have typed any character that is not supported by the character encoding, then Thunderbird warns you and offers to send the message using Unicode (UTF-8). Normally, you should accept the offer. If you ignore the warning and send the message anyway, then whoever receives your message might not be able to read what you have typed.

Thunderbird user interface

The user interface means the menus, folder pane, message-list pane, and other parts of Thunderbird that you interact with as a user.

The easiest way to change the user interface is by installing and using a theme.

Advanced users can control the fonts used in the Thunderbird interface by editing the userChrome.css file. For instance, this article explains how the change fonts used in menus and window panes. You'll find other examples among the visual customizations articles.

Bug reports

If you've come across a font-related bug in Thunderbird, please ask about it in the MozillaZine forums or search Bugzilla to see if it's already been reported.

  • Thunderbird UI uses two sets of terms for font width [1]
  • If you use a variable width font such as Verdana for your standard fixed width font, there may be wrapping problems when composing in plain text [2].
  • On Japanese WinXP, Thunderbird 1.5, switching between "Serif" and "Sans-serif" for "Proportional" font seems to be work only in the Compose window, not in the preview pane [3].

See also

External links

Wikipedia articles: