Windows Live Writer has no alternative, it is the best blogging client on desktop! It supports all leading blogging platforms (except Tumblr) and advanced formatting features.
The official plug-in gallery for Live Writer hosts many plug-ins to customize your experience. For Firefox users, there is a Blog This for Firefox plug-in which enables users to blog quickly from Firefox. It adds a button on Firefox’s navigation toolbar, and starts a new draft in Live Writer prepopulated with selected snippets from the current web page.
Also see: Firefox Add-on for Microsoft OneNote