Joomla: 2.5.28
Content Editor: JCE Editor 2.4.6

Goal: Embed a cool Wistia video in a Joomla 2.5 Article.

Problem: Joomla editor keeps scrambling <iframe> into <i-frame>. SO ANNOYING!

Solutions (for Joomla 2.5 and Joomla 3):

A) Joomla Global Configuration

1. In the Joomla! Global Configuration, click on the Text Filters tab.
2. For the Super Users group, or any other trusted user group, set Filter Type to No Filtering. Make sure that you only set this option for user groups that can be trusted as setting the Filter Type to No Filtering will essentially allow the user to include any html in an article.

Source: JCE Content Editor – IFrame removed on saving or editor toggle

B) RSFirewall Whitelist

Add the IP of the working PC you are using in the RSFirewall! whitelist (Components > RSFirewall! > Blacklist/Whitelist) – this way all the security filters and restrictions applied by the component will be ignored for your IP

Source: RSJoomla – Scrambled tags (iframe becomes i-frame)