Delete word to the left

`Ctrl` + `⬅ Backspace`

All hotkeys for Mozilla Thunderbird

Address book New address book contact	`Ctrl` + `N`
Address book Write new message to selected contacts	`Ctrl` + `M`
Editing message text Rewrap message text	`Ctrl` + `R`
Editing message text Remove named anchors	`Ctrl` + `↑ Shift` + `R`
Message functions Reply to list	`Ctrl` + `↑ Shift` + `L`
Message functions Forward message	`Ctrl` + `L`
Message functions Edit message as new	`Ctrl` + `E`
Message functions Get new messages for current account	`F5`
Message functions Get new messages for all accounts	`↑ Shift` + `F5`
Message functions Open message (in new window or tab)	`Ctrl` + `O`
Message functions Open message (in new window or tab)	`⤶ Enter`
Message functions (on message or folder) Open message or folder in a new tab in the background	`Mouse middle click`
Message functions then hold <keybs>Shift</keybs> while choosing: Open Message in New Tab	`Mouse right click`
Editing message text Paste as quotation	`Ctrl` + `↑ Shift` + `O`
Styling the message text Larger font size	`Ctrl` + `+`
Controlling the compose window Zoom in	`Ctrl` + `=`
Message functions Zoom in	`Ctrl` + `Mouse wheel up`
Styling the message text Smaller font size	`Ctrl` + `-`
Message functions Zoom out	`Ctrl` + `Mouse wheel down`
Controlling the compose window Reset zoom	`Ctrl` + `0`
Message functions Expand collapsed thread	`→`
Message functions Collapse expanded thread	`←`
Message functions Expand all threads	`*`
Message functions Collapse all threads	`\`
Message functions Newsgroups: Ignore or unignore thread	`K`
Message functions Newsgroups: Ignore or unignore subthread	`↑ Shift` + `K`
Message functions Newsgroups: Watch thread	`W`
Lightning: General Print	`Ctrl` + `P`
Writing messages Save draft	`Ctrl` + `S`
Managing messages View message source	`Ctrl` + `U`
Address book Select all (contacts or search text)	`Ctrl` + `A`
Editing message text Attach file	`Ctrl` + `↑ Shift` + `A`
Managing messages Toggle Caret browsing (select text with keyboard)	`F7`
Lightning: General Copy (selected events, tasks or text)	`Ctrl` + `C`
Lightning: General Cut (selected events, tasks or text)	`Ctrl` + `X`
Lightning: General Paste	`Ctrl` + `V`
Managing messages Drag message to destination folder to copy message to another folder (release mouse button before releasing Ctrl)	`Ctrl` + `Mouse movement`
Managing messages Move/Copy message to previous target folder again	`Ctrl` + `↑ Shift` + `M`
Managing messages Archive message	`A`
Editing message text Delete selected text, attachment, table cell contents or table	`Del`
Managing messages Delete message bypassing trash (no undo!)	`↑ Shift` + `Del`
Lightning: General Undo	`Ctrl` + `Z`
Lightning: General Redo	`Ctrl` + `Y`
Editing message text Rename attachment	`F2`
Tagging and marking messages to <keybs>9</keybs>: Add / remove tag	`1`
Tagging and marking messages Remove all tags from message	`0`
Tagging and marking messages Mark message as read / unread	`M`
Tagging and marking messages Mark thread as read	`R`
Tagging and marking messages Mark all read	`↑ Shift` + `C`
Tagging and marking messages Mark as read by date	`C`
Tagging and marking messages Mark as junk	`J`
Tagging and marking messages Mark as not junk	`↑ Shift` + `J`
Tagging and marking messages Add / remove star	`S`
Editing message text Insert link	`Ctrl` + `K`
Lightning: Tasks tab Filter tasks	`Ctrl` + `↑ Shift` + `K`
Lightning: Tasks tab Clear current tasks filter	`Esc`
Address book Address book advanced search	`Ctrl` + `↑ Shift` + `F`
Address book Address book quick filter	`Ctrl` + `F`
Editing message text Find again in current message	`Ctrl` + `G`
Editing message text Find again in current message	`F3`
Editing message text Find previous in current message	`Ctrl` + `↑ Shift` + `G`
Editing message text Find previous in current message	`↑ Shift` + `F3`
Moving between messages Go to Mail Start Page	`Alt` + `Home`
Moving between messages Scroll down current message, then go to next unread message	`Space`
Moving between messages Go to Next message	`F`
Moving between messages Go to Previous message	`B`
Moving between messages Go to Next unread message	`N`
Moving between messages Go to Previous unread message	`P`
Moving between messages Go to next unread thread (and mark current thread as read)	`T`
Moving between messages Go to next viewed message	`]`
Moving between messages Go to previous viewed message	`[`
Controlling Thunderbird windows and tabs Move to next UI element	`⭾ Tab`
Controlling Thunderbird windows and tabs Move to previous UI element	`↑ Shift` + `⭾ Tab`
Controlling the compose window Move to next main UI element	`F6`
Controlling the compose window Move to next main UI element	`Ctrl` + `F6`
Controlling the compose window Move to previous main UI element	`↑ Shift` + `F6`
Controlling the compose window Move to previous main UI element	`Ctrl` + `↑ Shift` + `F6`
Controlling the compose window Move to next main UI element	`Ctrl` + `⭾ Tab`
Controlling Thunderbird windows and tabs Next tab	`Ctrl` + `Page Down`
Controlling the compose window Move to previous main UI element	`Ctrl` + `↑ Shift` + `⭾ Tab`
Controlling Thunderbird windows and tabs Previous tab	`Ctrl` + `Page Up`
Lightning (calendar add-on) Mail & newsgroups home tab (tab 1)	`Ctrl` + `1`
Controlling Thunderbird windows and tabs to <keybs>8</keybs>: Go to tab 2 to 8	`Ctrl` + `2`
Controlling Thunderbird windows and tabs Last tab	`Ctrl` + `9`
Controlling Thunderbird windows and tabs Address book	`Ctrl` + `↑ Shift` + `B`
Controlling Thunderbird windows and tabs Saved files	`Ctrl` + `J`
Controlling Thunderbird windows and tabs Help	`F1`
Controlling Thunderbird windows and tabs Toggle message pane	`F8`
Controlling Thunderbird windows and tabs Toggle menu bar (if hidden)	`Alt`
Controlling Thunderbird windows and tabs Toggle menu bar (if hidden)	`F10`
Controlling Thunderbird windows and tabs Show context menu	`Context menu button`
Controlling Thunderbird windows and tabs Show context menu	`↑ Shift` + `F10`
Controlling Thunderbird windows and tabs Minimize current window	`Win` + `↓`
Controlling Thunderbird windows and tabs Close window or tab	`Ctrl` + `W`
Controlling Thunderbird windows and tabs Close window	`Alt` + `F4`
Controlling Thunderbird windows and tabs Close tab	`Ctrl` + `F4`
Controlling Thunderbird windows and tabs Undo close tab (restore and go to most recently closed tab)	`Ctrl` + `↑ Shift` + `T`
Writing messages Send message now	`Ctrl` + `⤶ Enter`
Writing messages Send message later	`Ctrl` + `↑ Shift` + `⤶ Enter`
Controlling the compose window Toggle contacts sidebar	`F9`
Controlling the compose window Zoom in	`Ctrl` + `Mouse wheel up`
Controlling the compose window Zoom out	`Ctrl` + `Mouse wheel down`
Editing message text Delete word to the right	`Ctrl` + `Del`
Editing message text Delete word to the left	`Ctrl` + `⬅ Backspace`
Editing message text (on table border) Select table	`Ctrl` + `Mouse left click`
Editing message text Drag mouse across cells of rows or columns to select table rows or columns	`Mouse movement`
Editing message text Find and replace text in current message	`Ctrl` + `H`
Editing message text Check spelling	`Ctrl` + `↑ Shift` + `P`
Styling the message text Larger font size	`Ctrl` + `>`
Styling the message text Larger font size	`Ctrl` + `,`
Styling the message text Smaller font size	`Ctrl` + `<`
Styling the message text Smaller font size	`Ctrl` + `.`
Styling the message text Text style bold	`Ctrl` + `B`
Lightning (calendar add-on) New event	`Ctrl` + `I`
Styling the message text Discontinue or remove text styles	`Ctrl` + `↑ Shift` + `Y`
Styling the message text Discontinue or remove text styles	`Ctrl` + `Space`
Styling the message text Increase indent	`Ctrl` + `]`
Styling the message text Decrease indent	`Ctrl` + `[`
Miscellaneous Clear history	`Ctrl` + `↑ Shift` + `Del`
Lightning (calendar add-on) Show or hide Today pane	`F11`
Lightning (calendar add-on) Calendar tab	`Ctrl` + `↑ Shift` + `C`
Lightning (calendar add-on) Tasks tab	`Ctrl` + `↑ Shift` + `D`
Lightning (calendar add-on) New task	`Ctrl` + `D`
Lightning: Calendar tab Go to Today	`Alt` + `End`
Lightning: Calendar tab Day view	`Alt` + `1`
Lightning: Calendar tab Week view	`Alt` + `2`
Lightning: Calendar tab Multiweek view	`Alt` + `3`
Lightning: Calendar tab Month view	`Alt` + `4`