diff --git a/src/SlashCommands.tsx b/src/SlashCommands.tsx
index 403ecf5772..80fc98f97d 100644
--- a/src/SlashCommands.tsx
+++ b/src/SlashCommands.tsx
@@ -1305,19 +1305,17 @@ export const Commands = [
             description: effect.description(),
             args: '<message>',
             runFn: function(roomId, args) {
-                return success((async () => {
-                    if (!args) {
-                        args = effect.fallbackMessage();
-                        MatrixClientPeg.get().sendEmoteMessage(roomId, args);
-                    } else {
-                        const content = {
-                            msgtype: effect.msgType,
-                            body: args,
-                        };
-                        MatrixClientPeg.get().sendMessage(roomId, content);
-                    }
-                    dis.dispatch({ action: `effects.${effect.command}` });
-                })());
+                let content: IContent;
+                if (!args) {
+                    content = ContentHelpers.makeEmoteMessage(effect.fallbackMessage());
+                } else {
+                    content = {
+                        msgtype: effect.msgType,
+                        body: args,
+                    };
+                }
+                dis.dispatch({ action: `effects.${effect.command}` });
+                return successSync(content);
             },
             category: CommandCategories.effects,
             renderingTypes: [TimelineRenderingType.Room],
diff --git a/src/components/views/rooms/EditMessageComposer.tsx b/src/components/views/rooms/EditMessageComposer.tsx
index 9a0e4d1ea8..83c494bca7 100644
--- a/src/components/views/rooms/EditMessageComposer.tsx
+++ b/src/components/views/rooms/EditMessageComposer.tsx
@@ -337,7 +337,7 @@ class EditMessageComposer extends React.Component<IEditMessageComposerProps, ISt
                         return; // errored
                     }
 
-                    if (cmd.category === CommandCategories.messages) {
+                    if (cmd.category === CommandCategories.messages || cmd.category === CommandCategories.effects) {
                         editContent["m.new_content"] = content;
                     } else {
                         shouldSend = false;
diff --git a/src/components/views/rooms/SendMessageComposer.tsx b/src/components/views/rooms/SendMessageComposer.tsx
index a8e087e451..6750343a0d 100644
--- a/src/components/views/rooms/SendMessageComposer.tsx
+++ b/src/components/views/rooms/SendMessageComposer.tsx
@@ -358,12 +358,13 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
                     return; // errored
                 }
 
-                if (cmd.category === CommandCategories.messages) {
+                if (cmd.category === CommandCategories.messages || cmd.category === CommandCategories.effects) {
                     attachRelation(content, this.props.relation);
                     if (replyToEvent) {
                         addReplyToMessageContent(content, replyToEvent, {
                             permalinkCreator: this.props.permalinkCreator,
-                            includeLegacyFallback: true,
+                            // Exclude the legacy fallback for custom event types such as those used by /fireworks
+                            includeLegacyFallback: content.msgtype?.startsWith("m.") ?? true,
                         });
                     }
                 } else {
diff --git a/src/editor/commands.tsx b/src/editor/commands.tsx
index 279dfcc1a0..f3847e46b3 100644
--- a/src/editor/commands.tsx
+++ b/src/editor/commands.tsx
@@ -65,7 +65,7 @@ export async function runSlashCommand(
     let error = result.error;
     if (result.promise) {
         try {
-            if (cmd.category === CommandCategories.messages) {
+            if (cmd.category === CommandCategories.messages || cmd.category === CommandCategories.effects) {
                 messageContent = await result.promise;
             } else {
                 await result.promise;