Remove Firefox addons/extensions

These are not found on the specified server.

Author: BanzaiMan

user/apps.md

@@ -351,26 +351,6 @@ By excellenteasy
 
 - [website](https://chrome.google.com/webstore/detail/github-status/mgbkbopoincdiimlleifbpfjfhcndahp)
 
-## Mozilla Firefox
-
-### GitHub+Travis
-
-![chrome-github-travis](/images/apps/chrome-github-travis.jpg){:.app}
-
-Display build status next to project name on GitHub<br>
-By David Burns
-
-- [website](https://addons.mozilla.org/en-US/firefox/addon/githubtravis/)
-
-### Link to Travis Lite
-
-![firefox-travis-lite](/images/apps/firefox-travis-lite.jpg){:.app}
-
-Add a links to corresponding Travis Lite page<br>
-By Nigel Babu
-
-- [website](https://addons.mozilla.org/en-US/firefox/addon/link-to-travis-lite/)
-
 ## Opera
 
 ### GitHub+Travis

user/browser-extensions.md

@@ -12,10 +12,6 @@ layout: en
 
 [Universal Build Status Extension for Chrome](https://chrome.google.com/webstore/detail/github-status/mgbkbopoincdiimlleifbpfjfhcndahp) displays the latest build status from GitHub's statuses API next to the project name.
 
-### Firefox
-
-[Travis CI Build Status Extension for Firefox](https://addons.mozilla.org/en-US/firefox/addon/githubtravis/) displays the build status icon next to the project name on GitHub.
-
 ### Opera
 
 [Travis CI Build Status Extension for Opera](https://addons.opera.com/en/extensions/details/travisgithub/) displays the build status icon next to the project name on GitHub project/user pages and provides button for monitoring build status of user-defined projects. It also shows the build status of pull requests tested by the Travis Bot.