diff --git a/chat/components/public/prplIProtocol.idl b/chat/components/public/prplIProtocol.idl
index 5f7686878a..9d9eeadbd2 100644
--- a/chat/components/public/prplIProtocol.idl
+++ b/chat/components/public/prplIProtocol.idl
@@ -51,11 +51,23 @@ interface prplIProtocol: nsISupports {
    */
   Array<prplIPref> getOptions();
 
+  /**
+   * String to put in front of the full account username identifier. Usually
+   * an empty string.
+   */
+  readonly attribute AUTF8String usernamePrefix;
+
   /**
    * @returns an array of prplIUsernameSplit
    */
   Array<prplIUsernameSplit> getUsernameSplit();
 
+  /**
+   * Split a username into its parts without separators (or prefix).
+   * Returns an empty array if the username can not be split.
+   */
+  Array<AUTF8String> splitUsername(in AUTF8String aName);
+
   /**
    * Descriptive text used in the account wizard to describe the username.
    */
diff --git a/chat/components/src/imAccounts.jsm b/chat/components/src/imAccounts.jsm
index ec8ffab6ad..2af240bcb9 100644
--- a/chat/components/src/imAccounts.jsm
+++ b/chat/components/src/imAccounts.jsm
@@ -108,6 +108,9 @@ UnknownProtocol.prototype = {
   getOptions() {
     return [];
   },
+  get usernamePrefix() {
+    return "";
+  },
   getUsernameSplit() {
     return [];
   },
diff --git a/chat/modules/jsProtoHelper.jsm b/chat/modules/jsProtoHelper.jsm
index cb3f19af4d..857403f121 100644
--- a/chat/modules/jsProtoHelper.jsm
+++ b/chat/modules/jsProtoHelper.jsm
@@ -1169,6 +1169,7 @@ var GenericProtocolPrototype = {
     }
     return purplePrefs;
   },
+  usernamePrefix: "",
   getUsernameSplit() {
     if (!this.usernameSplits || !this.usernameSplits.length) {
       return [];
@@ -1176,6 +1177,41 @@ var GenericProtocolPrototype = {
     return this.usernameSplits.map(split => new UsernameSplit(split));
   },
 
+  /**
+   * Protocol agnostic implementation that splits the username by the pattern
+   * defined with |usernamePrefix| and |usernameSplits| on the protocol.
+   * Prefers the first occurence of a separator.
+   *
+   * @param {string} aName - Username to split.
+   * @returns {string[]} Parts of the username or empty array if the username
+   *   doesn't match the splitting format.
+   */
+  splitUsername(aName) {
+    let remainingName = aName;
+    if (this.usernamePrefix) {
+      if (!remainingName.startsWith(this.usernamePrefix)) {
+        return [];
+      }
+      remainingName = remainingName.slice(this.usernamePrefix.length);
+    }
+    if (!this.usernameSplits || !this.usernameSplits.length) {
+      return [remainingName];
+    }
+    const parts = [];
+    for (const split of this.usernameSplits) {
+      if (!remainingName.includes(split.separator)) {
+        return [];
+      }
+      const separatorIndex = remainingName.indexOf(split.separator);
+      parts.push(remainingName.slice(0, separatorIndex));
+      remainingName = remainingName.slice(
+        separatorIndex + split.separator.length
+      );
+    }
+    parts.push(remainingName);
+    return parts;
+  },
+
   registerCommands() {
     if (!this.commands) {
       return;
diff --git a/chat/protocols/irc/irc.jsm b/chat/protocols/irc/irc.jsm
index 3f7507d23f..a0c7ea252a 100644
--- a/chat/protocols/irc/irc.jsm
+++ b/chat/protocols/irc/irc.jsm
@@ -995,9 +995,9 @@ function ircAccount(aProtocol, aImAccount) {
   this.conversations = new NormalizedMap(this.normalize.bind(this));
 
   // Split the account name into usable parts.
-  let splitter = this.name.lastIndexOf("@");
-  this._accountNickname = this.name.slice(0, splitter);
-  this._server = this.name.slice(splitter + 1);
+  const [accountNickname, server] = this.protocol.splitUsername(this.name);
+  this._accountNickname = accountNickname;
+  this._server = server;
   // To avoid _currentServerName being null, initialize it to the server being
   // connected to. This will also get overridden during the 001 response from
   // the server.
@@ -2362,6 +2362,11 @@ ircProtocol.prototype = {
     },
   ],
 
+  splitUsername(aName) {
+    let splitter = aName.lastIndexOf("@");
+    return [aName.slice(0, splitter), aName.slice(splitter + 1)];
+  },
+
   options: {
     port: {
       get label() {
diff --git a/mail/components/im/content/imAccountWizard.js b/mail/components/im/content/imAccountWizard.js
index 7bf9d9a174..c4edadbc90 100644
--- a/mail/components/im/content/imAccountWizard.js
+++ b/mail/components/im/content/imAccountWizard.js
@@ -91,16 +91,29 @@ var accountWizard = {
     }
   },
 
+  /**
+   * Builds the full username from the username boxes.
+   *
+   * @returns {string} assembled username
+   */
   getUsername() {
+    let usernameBoxIndex = 0;
+    if (this.proto.usernamePrefix) {
+      usernameBoxIndex = 1;
+    }
     // If the first username input is empty, make sure we return an empty
     // string so that it blocks the 'next' button of the wizard.
-    if (!this.userNameBoxes[0].value) {
+    if (!this.userNameBoxes[usernameBoxIndex].value) {
       return "";
     }
 
     return this.userNameBoxes.reduce((prev, elt) => prev + elt.value, "");
   },
 
+  /**
+   * Check that the username fields generate a new username, and if it is valid
+   * allow advancing the wizard.
+   */
   checkUsername() {
     var wizard = document.querySelector("wizard");
     var name = accountWizard.getUsername();
@@ -116,6 +129,28 @@ var accountWizard = {
     duplicateWarning.hidden = !exists;
   },
 
+  /**
+   * Takes the value of the primary username field and splits it if the value
+   * matches the split field syntax.
+   */
+  splitUsername() {
+    let usernameBoxIndex = 0;
+    if (this.proto.usernamePrefix) {
+      usernameBoxIndex = 1;
+    }
+    let username = this.userNameBoxes[usernameBoxIndex].value;
+    let splitValues = this.proto.splitUsername(username);
+    if (!splitValues.length) {
+      return;
+    }
+    for (const box of this.userNameBoxes) {
+      if (box instanceof Element) {
+        box.value = splitValues.shift();
+      }
+    }
+    this.checkUsername();
+  },
+
   selectProtocol() {
     var protoList = document.getElementById("protolist");
     var id = protoList.selectedItem.value;
@@ -153,11 +188,21 @@ var accountWizard = {
     input.addEventListener("input", event => {
       this.checkUsername();
     });
+    // Only add the split logic to the first input field
+    if (!this.userNameBoxes) {
+      input.addEventListener("blur", event => {
+        this.splitUsername();
+      });
+    }
     grid.appendChild(input);
 
     return input;
   },
 
+  /**
+   * Builds the username input boxes from the username split defined by the
+   * protocol.
+   */
   showUsernamePage() {
     var proto = this.proto.id;
     if ("userNameBoxes" in this && this.userNameProto == proto) {
@@ -191,6 +236,12 @@ var accountWizard = {
     var label = bundle.getString("accountUsername");
     this.userNameBoxes = [this.insertUsernameField("name", label, grid)];
     this.userNameBoxes[0].emptyText = emptyText;
+    let usernameBoxIndex = 0;
+
+    if (this.proto.usernamePrefix) {
+      this.userNameBoxes.unshift({ value: this.proto.usernamePrefix });
+      usernameBoxIndex = 1;
+    }
 
     for (let i = 0; i < splits.length; ++i) {
       this.userNameBoxes.push({ value: splits[i].separator });
@@ -200,7 +251,7 @@ var accountWizard = {
         this.insertUsernameField("username-split-" + i, label, grid, defaultVal)
       );
     }
-    this.userNameBoxes[0].focus();
+    this.userNameBoxes[usernameBoxIndex].focus();
     this.userNameProto = proto;
     this.checkUsername();
   },