If you are a blogger and make use of Windows Live Writer (WLW) to publish posts then the WLW BlogThis plugin for Firefox can be really useful.The Blog This for Firefox adds a button to Firefox which starts a new Windows Live Writer blog post prepopulated with content and title from the current web page.

but the plugin works with Firefox 2.0 only, Here’s how you could make it work with Firefox 3.0+.

Method 1 :

1. After installing the plugin from the FFBlogThis.msi
2. Start Notepad
3. Open this file:
   C:\Program Files\Windows Live\Writer\BlogThis\Mozilla Firefox\install.rdf
4. Edit the line
   <em:maxVersion>2.0+</em:maxVersion>
   to
   <em:maxVersion>3.0+</em:maxVersion>
5. Rename install.rdf to install.rdf.gone
6. Exit Firefox, if it’s running
7. Start Firefox
8. Exit Firefox
9. Rename install.rdf.gone back to install.rdf
10. Start Firefox

Requires .NET Framework 1.1 and WLW 1.0.x and above

Download WLW Blogthis Plugin

Source  : jcheng

Method 2 :

1. Type “about:config” in the address bar.
2. Right click on the window and select New->Boolean and type “extensions.checkCompatibility” and set the value as “false”.
3. The WLW BlogThis plugin For firefox  should start working.

Method 3 :

Using the Nightly Tester Tools 2.0.2 addon to overcome the incompatibility of the plugin.

There’s also a experimental plugin of version 2.0 @ Mozilla for which you have to login and download.