How does omnibox addSuggest work in private mode?

I tried omnibox with the following code from MDN. When I trying, I temporarily loaded manifest.json from about:debugging. This worked in a normal browser, and typing cs a show a some suggestion.

However, this suggestion feature is not working in private mode. This did not change even if I allowed it to run in a private window. How can I get the omnibox suggestion feature to work in private mode?

I also tried check “Show search suggestions in Private Windows” option, but that didn’t change the results. I also found that execute the simple console.log function in private mode didn’t work for the onInputChange event.

Can you upload a test extension that demonstrates this behavior?

Thanks for reply. I’m using below source code. This temporary extension was ran in the following environment:

  • Windows 10
  • Firefox 84.0.2 (64 bit)


  "manifest_version": 2,
  "name": "Custom suggestion",
  "version": "1.0",
  "description": "Custom suggestion using omnibox.",
  "background": {
    "scripts": [
  "omnibox": {
    "keyword": "cs"
  "permissions": [


// ref.
    description: "Type the name of a CSS property"

Very short list of a few CSS properties.
const props = [

const baseURL = "";

Return an array of SuggestResult objects,
one for each CSS property that matches the user's input.
function getMatchingProperties(input) {
    var result = [];

    for (prop of props) {
        if (prop.indexOf(input) === 0) {
            let suggestion = {
                content: baseURL + prop,
                description: prop
        } else {
            if (result.length != 0) {
                return result;
    return result;

browser.omnibox.onInputChanged.addListener((input, suggest) => {

browser.omnibox.onInputEntered.addListener((url, disposition) => {
    switch (disposition) {
        case "currentTab":
        case "newForegroundTab":
        case "newBackgroundTab":
            browser.tabs.create({url, active: false});

You can also zip the complete extension and attach it to your reply.
The Upload icon is the 7th from the left (arrow pointing up)

I have attached a zip file that contains the minimal source code to reproduce my problem. (1.1 kb)

This bug was fixed in Firefox 110 (bug 1779400).