Font Inspector (WebExtension) – Get this Extension for 🦊 Firefox (en-US)

Download Font Inspector (WebExtension) for Firefox. Click on any element to get the font info in a page popup

Tree Style Tab For Chrome

Font Inspector (WebExtension) – Get this Extension for 🦊 Firefox (en-US)

Extension Inspector – Get this Extension for 🦊 Firefox (en-US)

Your second extension - Mozilla

javascript - Browser Extension Manifest v3 with webextension-polyfill does not allow browser.browserAction.onClicked (on Chrome) - Stack Overflow

PopUp – Get this Extension for 🦊 Firefox (en-US)

NoScript Add-On Updated for Firefox 57 and the New WebExtensions API

Font Finder (revived) – Get this Extension for 🦊 Firefox (en-US)

React Developer Tools – Get this Extension for 🦊 Firefox (en-US)

WebExtension X-Ray – Get this Extension for 🦊 Firefox (en-US)

Errors using webextension-polyfill to make a cross-browser add-on - Development - Mozilla Discourse

Enforce Browser Fonts – Get this Extension for 🦊 Firefox (en-US)