Is there a plug-in for Firefox that will bring it close to the ease of use of the Composer-mode WYSIWYG functionality of the browser Mozilla Sea Monkey?

Background: The IT police in our 400,000-employee public organization have declared war on SeaMonkey as a security risk and it is systematically deleting it. My office has used it for nearly 10 years to update and grow gigabytes of interlinked local intranet html files. One might call it a website, but that would make our little underground railroad subject to a bunch more IT rules. This has little artwork, so the beauty of SeaMonkey was that any idiot -- perhaps already using SeaMonkey as their browser -- could update a statistic or add the latest issue position/development on any page that he/she is browsing with a simple Control-E (or Cmd-E for Mac), going from Browse to Edit mode. The height of the learning curve was menu-building and cross-references, which meant showing a newbie how to embed a hyperlink to another page or web resource. No learning a complex html program. And when something was a little messed up and the raw html required work by a more experienced user, it wasn't cluttered with all that useless MSO code that MS Word interjects in the Internet Explorer editing function. Can we use Firefox this way?