From MozillaZine Knowledge Base

To get rid of the colored bars used to mark quoted text in messages, so that quoted text will instead be marked with ">", either install the Quote Colors extension and disable "Graphical Quoting" in its options dialog or put the following code in your "userContent.css" and "user.js" files, respectively.

In userContent.css, insert:

blockquote[type=cite] {
   padding-bottom: 0 !important;
   padding-top: 0 !important;
   padding-left: 0 !important;
   border-left: none !important;
   border-right: none !important;
} 

In user.js, insert:

user_pref("mail.quoted_graphical", false);
user_pref("mail.quoteasblock", false);
user_pref("mailnews.display.disable_format_flowed_support", true);

format=flowed

The format=flowed standard, which is defined by RFC 3676, allows an e-mail application to automatically rewrap plain-text messages to fit into the window width for display and when replying. This rewrapping also rearranges the '>' characters of recognized quotes, and places them at the beginning of each rewrapped line. You can find details of Mozilla's implementation here and here (the latter may be somewhat out of date). This forum post describes compatibility problems between Thunderbird's format=flowed and other e-mail programs.

See also

• Reply above quoted message
• Reply header settings
• Message templates

External links

• Mozillazine forum thread for further discussion
• Using different quote level colors from mozilla.org's Thunderbird Help
• The Quote Colors extension has an option to restore the traditional quote character.
• The QuoteAndComposeManager extension has options to modify the quoting style when composing e-mails.