Forgive me if TiddlySnip already does this, but as a user, this scenario would be useful to me:
Browser plugin lets me create a tiddler in a bag on my tiddlyweb instance, with the current URL as the body and either the title of the web page or my own text as the title.
I should be able to specify the bag, any authentication info, and the path to it, in the plugin's persisted options.