When editing inside <pre> blocks, spaces at the beginning of lines are inserted as instead of as a space. These break the live sample system, since isn't legal in CSS, for example. The best fix would be to make it not do in <pre> blocks like this.
Commits pushed to master at https://github.com/mozilla/kuma https://github.com/mozilla/kuma/commit/f36cb4bd0503cba07dbde2eb105562dda6b02033 fix bug 811768 - Prevents nbsp;'s in PRE tags https://github.com/mozilla/kuma/commit/05d2bfdaa99b8c657d9d524622c31c31deaf17d8 Merge pull request #705 from darkwing/pre-tabs-811768 fix bug 811768 - Prevents nbsp;'s in PRE tags
verified fixed https://developer.allizom.org/en-US/docs/WebSockets