Here is how you can use the Performancing plugin for Firefox to post a subtext powered blog.

1) Download performancing here.

2) Assuming you have your Subtext-powered blog up and running, start Performancing by clicking on the icon in your Firefox browser status bar.

3) Click the “Add” button in the Blog tab of performancing.

4) Click “Manually Configure”

5) Choose “Custom Blog” from the drop down where it asks you “What Blogging Service do you want to add?”. Click NEXT

6) Choose “MetaWeblog API” from the blog system list.

7) In the Server API URL: type in the following
http://[your subtext blog url]/services/metablogapi.aspx

for example:
http://Ihaveacoolblog.com/services/metablogapi.aspx

Click NEXT

Type in your Subtext admin username and password, click NEXT

9) You should be all set. Enjoy.