| Event Spy Too | | - | | |
| Element Digger | | - | | |
| EditCSS | | - | | |
| Dust-Me Selectors | | - | | |
| Dummy Images | | - | | |
| Display ＃Anchors | | - | | |
| Developer Tools - toolbar button | | - | | |
| DevTools toolbar items | | - | | |
| DevPrefs | | - | | |
| Dev Buttons | | - | | |
| Default Responsive Design View | | - | | |
| Deepest Sender | | - | | |
| DOM Inspector Toolbar Button | | - | | |
| Copy as Markdown | | - | | |
| Copy Link as HTML or Markdown Code | | - | | |
| Copy HTML | | - | | |
| CookieWatcher | | - | | |
| Context Font | | - | | |
| Console2 | | - | | |
| Colorizer | | - | | |
| Colorblind Design | | - | | |
| ColorZilla | | - | | |
| CodeBurner for Firefox | | - | | |
| CodeBurner for Firebug | | - | | |
| Chrome List | | - | | |
| CacheToggle | | - | | |
| CSSsir | | - | | |
| CSSViewer | | - | | |
| CSS Usage | | - | | |
| CSS Reloader | | - | | |
| CSS Reload | | - | | |
| Browser Console Button | | - | | |
| Browser Calories | | - | | |
| Blank Scratchpad | | - | | |
| Auto-Open Browser Console | | - | | |
| Auto Reload | | - | | |
| Animat | | - | | |
| Affilorama SEO Toolbar | | - | | |
| Advanced Frame Designer | | - | | |
| Adobe BrowserLab for Firebug | | - | | |
| Add-on SDK Examples | | - | | |
| AdMatrix Analytics | | - | | |
| Acebug | | - | | |
| ASP.NET Viewstate Viewer | | - | | |
| AMF Explorer | | - | | |