| Save Back to File from DOM | | - | | |
| Scratchpad | | - | | |
| Scratchpad Button | | - | | |
| Scratchpad Editor | | - | | |
| Screen sizes | | - | | |
| Selenium IDE | | - | | |
| SenSEO | | - | | |
| Server Switcher | | - | | |
| Sharp Color Picker | | - | | |
| Show external css／js files | | - | | |
| Simple Base64 | | - | | |
| Simple Markup Validator | | - | | |
| Simple Storage Editor for Addon SDK | | - | | |
| Site to Panel | | - | | |
| SiteCheckr | | - | | |
| SourceEditor | | - | | |
| Speed Page | | - | | |
| SpeedView | | - | | |
| Strike Out Nofollow Links | | - | | |
| Style Editor | | - | | |
| Style Guide Generator | | - | | |
| SummerCSS | | - | | |
| Tag Attribute Finder | | - | | |
| Text To Code Ratio | | - | | |
| TextToTag | | - | | |
| ThumbnailCopy | | - | | |
| Toggle Development Profile Prefs | | - | | |
| Toggle Paint Flashing | | - | | |
| TortoiseSVN Menu | | - | | |
| Try IT Yourself HTML5 editor | | - | | |
| TypeGauge | | - | | |
| UxU - UnitTest.XUL | | - | | |
| Validate Me | | - | | |
| Validator | | - | | |
| Validaty | | - | | |
| View Scratchpad As HTML | | - | | |
| View Scratchpad As HTML Jetpack | | - | | |
| View Source | | - | | |
| View Source Chart | | - | | |
| WCAG Contrast checker | | - | | |
| WSDL Preview | | - | | |
| Wappalyzer | | - | | |
| WatchPug | | - | | |
| Web Console | | - | | |
| Web Developer | | - | | |
| Web Developer Toolbar Button | | - | | |
| Web Metrics Framework | | - | | |
| Web page to source code ＆ viceversa | | - | | |
| Wikipedia-References-Creator | | - | | |
| X-Ray | | - | | |
