bc100-autofill/bg.js

browser.runtime.onInstalled.addListener((ev) => {
    if (ev.reason == "update") {
        initialiseSettings();
        updateIsSignificant(ev.previousVersion).then(
            v => {
                if (v) launchInfoPage();
            }
        )
    } else if (ev.reason == "install") {
        initialiseSettings().then(() => browser.runtime.openOptionsPage());
    }
})

async function updateIsSignificant(previousVersion) {
    const significantUpdates = ["0.1.0", "0.2.0", "0.3.0"];
    let currentVersion = (await browser.management.getSelf()).version;
    return (currentVersion in significantUpdates) || currentVersion.endsWith('.0'); // semver! :D
}
function launchInfoPage(){
    browser.tabs.create({url: "/changelog.htm", active: false})
}

async function initialiseSettings(){
    let defaultSettings = {"enable": true, "showChangelog": true};
    const presentSettings = await browser.storage.sync.get();
    defaultSettings = Object.fromEntries(Object.entries(defaultSettings).filter((k, v) => !(k in presentSettings)));
    await browser.storage.sync.set(defaultSettings);
}