Live HTTP Headers
Monitor all HTTP/HTTPs traffic from your browser.
Modify Header Value
Add, modify or remove a header for any request on desired domains.
BuiltWith Technology Profiler
Find out what the website you are visiting is built with using this extension.
View all HTTP Requests and Responses sent between the Web browser and the Web server.
Use Redux DevTools in the DevTools
Disable cookies for current domain.
Google Analytics Debugger
A browser extension for debugging Google Analytics tracking code
Picture in Play
Indicates whether the `picture` element is in use on a page.
Browse JSON like you do it in Finder.
Firebug Lite for Opera 15+
This extension allows you to add your own custom website specific CSS style sheets.
Live editor for CSS and LESS - Magic CSS
Live preview of CSS/LESS code with an in-page editor. Autocomplete, convert LESS to CSS, beautify, minify, CSS reloader, linter, ...
Quickly view the HTTP headers of the current tab.
Edit the Page
Toggles the 'Design Mode' so that you can edit the contents of the page.
Website Analysis & SEO Tool
Website SEO audit tool that provides website analysis in SEO, performance, validity, security, accessibility and other criteria.
Browserling - Cross-browser testing
Cross-browser test websites in the most popular browsers such as Internet Explorer, Edge, Chrome, Firefox, Safari and Opera. Try for free!
Right Click Validator
Right click on any webpage to validate it using the W3 NUValidator service.
WordPress Theme and Plugins Detector
This tool detects theme and plugins used on WordPress sites and displays information about them.
Remove cookie(s) for the current domain
Remove cookie(s) for the current site with just one click
Get Thumbnails or Image to video YouTube
A small extension to validate the markup of current tab
Website Color Changer
Extends the Developer Tools, adding a sidebar for colors manipulation
Corser - Authorize CORS requests
Cross-browser extension for authorizing cross-origin resource sharing (CORS) requests. This extension can be installed on browsers supporting the WebExtensions API (https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions) It intercepts all CORS requests and responses headers, and records/adds/changes their values so as to authorized unauthorized CORS requests. Use this extension only for testing purposes
This will take the URL of the current tab and send it to PageSpeed Insights for a web performance analysis.
SEO Analysis with Seoptimer
Just one click to SEO Analysis with Seoptimer
Edit with Adobe Photoshop
Adds a context menu item to send image links directly to Adobe Photoshop photo editor
ChroPath for Opera
AutonomIQ offers a developers platform ChroPath to generate and validate unique selectors like relative xpath with iframe support
This extension predicts rating changes for Codeforces. It shows approximate deltas during and after the contest.