// Show the user agent in the message header
user_pref("mailnews.headers.showUserAgent", true);
// Change default paper size from US-Letter to A4
user_pref("print.postscript.paper_size", "A4");
Customization: userChrome.css
/* Change the font weight of account names on the folders pane from bold to normal */
treechildren:-moz-tree-cell-text(folderNameCol, isServer-true) {font-weight: normal !important; }
/* Change the font weight of subfolders with unread messages from bold to normal */
treechildren:-moz-tree-cell-text(hasUnreadMessages-true) {font-weight: normal !important; }
/* Change the line height of the header to, e.g., 1.25 em */
.headerName {margin: 0 !important; line-height: 1.25em !important; }
.headerValue {margin: 0 !important; line-height: 1.25em !important; }
.headerValueBox {margin: 0 !important; line-height: 1.25em !important; }
/* Change the font weight of the value of the subject line in a message header from bold to normal */
.subjectvalue {font-weight: normal !important; }
Customization: userContent.css
/* Leave the margin of, e.g., 0.75em in the message pane */
body {margin: 1.25em !important; }
/* Change the line height of a message body to, e.g., 1.25em */
body {line-height: 1.25em !important; }
Display HTML messages as plain text:
View -> Message Body As -> click "Plain Text"
Compose messages in plain text format:
Tools -> Account Settings -> Composition & Addressing -> Composition -> uncheck "Compose messages in HTML format
Start your reply below the quote:
Tools -> Account Settings -> Composition & Addressing -> Composition -> check "Automatically quote the original message when replying" and choose "Then, start my reply below the quote"
Disable the display of emoticons as graphics:
Tools -> Options -> Display -> Formatting -> Plain Text Messages -> uncheck "Display emoticons as graphics"
Use monospace fonts:
Tools -> Options -> Display -> Formatting -> Plain Text Messages -> check "Fixed width font"
Minimum font size:
Tools -> Options -> Display -> Fonts -> set "Minimum font size" for each character set
Default character encoding:
Tools -> Options -> Display -> Fonts -> Languages; choose a character encoding from the drop-down menu
Block loading of remote images:
Tools -> Options -> Privacy -> General -> check "Block loading of remote images in mail messages"
Include a server when getting new mail:
Tools -> Account Settings -> <server> -> Server Settings -> Advances -> check "Include this server when getting new mail"
BiDi Mail UI [extension for right-aligning plain text messages]
Transliterator [extension for transliterating Cyrillic and some other non-Roman scripts used for Russian, etc. with a US English or any other Roman-script keyboard]
Dictionaries [dictionaries for the spell checker in various languages]