If you find any bugs, please try to find as much informations as possible to help to resolve it. First I will need your operating system (Windows 7, Ubuntu Linux, etc.) and browser version (Firefox 9.0.1). If you know how to reproduce, tell me the steps. If something is just not working for you please do the following steps: Before you do anything the best would be if you change your home page to "about:blank". (here is an article about how you can do that: http://support.mozilla.org/en-US/kb/How%20to%20set%20the%20home%20page) Close all open tabs, then restart the Firefox. Open the error console: Tools/Web Development/Error Console (or press Ctrl + Shift + J) Here select the Error button, and check that is there any error messages which mention GRW or grwatcher or Google Reader Watcher. Also you can check the messages tab, maybe there you can find some messages. If the error happens only after some specific movements (for example checking for new feeds), clear the window and do the thing.
You can also try to create a new profile and install only this extension. More details about how to create new profile: http://kb.mozillazine.org/Profile_manager. Don't change any setting, only what necessary, because maybe one of the settings causes the issue.