This happens due to the reason mentioned in this page. -->
http://adblockplus.org/blog/web-pages-accessing-chrome-is-forbidden . I found it after a bit of searching on google.
Anyway you can fix the problem by editing the siteadvisor extension a bit. All you need to do is add the line
content safe jar:chrome/safe.jar!/content/ contentaccessible=yes after
content safe jar:chrome/safe.jar!/content/ in the
chrome.manifest file. To access this file you need to download the siteadvisor extension and extract the contents of the safe.xpi file using winzip or something similar. Then open the
chrome.manifest file using notepad and add that line to it as mentioned above. Then you need to zip up the folder containing the files that you extracted and then rename the zip file to a xpi file. Then drag and drop that file into firefox to install the modified extension.
🙂Here's the modified version of the extension in case you don't want to do the above yourself. It also contains another modification so that the status bar doesn't get thicker after you install SiteAdvisor.