Browser: Firefox v3.5.7 (released 01/05/2010)
Web Software: WordPress 2.9.1 (released 01/04/2010)

Problem: After updating both the browser and the CMS software, it appears that adding a new post or editing an existing post causes the browser to reload. The result of this reload is a bar of web form buttons akin to those used when viewing the HTML of the post.

Current Workaround: Use Google Chrome for posting.

UPDATE (01/06/2010) – Tinkering with the plug-ins revealed that the Myspace extension was messing things up.  Disabling Myspace & the OpenID extensions resolved this issue.  Also, updated the default post/page editor with FCKEditor.