devtools.inspectedWindow.tabId

The ID of the tab that this instance of the devtools is attached to, represented as a number.

This can be sent to the extension's background page, so that background page can use the tabs API to interact with the tab:

// devtools-panel.js

const scriptToAttach = "document.body.innerHTML = 'Hi from the devtools';";

attachContentScriptButton.addEventListener("click", () => {
  browser.runtime.sendMessage({
    tabId: browser.devtools.inspectedWindow.tabId,
    script: scriptToAttach
  });
});
// background.js

function handleMessage(request, sender, sendResponse) {
  browser.tabs.executeScript(request.tabId, {
    code: request.script
  });
}

browser.runtime.onMessage.addListener(handleMessage);

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
tabId
Yes
79
54
?
Yes
No
?
?
No
?
?
?

Note: This API is based on Chromium's chrome.devtools API.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools/inspectedWindow/tabId