Quick issue about Firefox extension development using tabs

We are newbies on firefox extension development and have an small issue: - We are working with "loading event" so we know when a new page is opened and we change 开发者_运维问答our toolbar accordingly, but we don't know how to get "change tab event", so we can't change our toolbar when user returns to a previously opened tab. Will you explain us how to get a notification when user changes the tab in their browser?

Further information: - we are developing a toolbar that shows a message for current page:

1. If you go to google.com it shows "google.com is OK".
2. When user opens a new tab, this function get executed properly and shows a message for new url (ie. "example.com is OK")
3. When user comes back to first tab (where you have opened google.com) we don't know how to change toolbar message and show again "google.com is OK". Our toolbar currently shows message from latest opened window instead of switching accordingly to the tab where you currently are (when you go back to google.com tab it still shows 'example.com is OK). We don't know how to get "change tab" event.

I have been searching a lot but couldn't find an answer, could you help??

thanks

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See Firefox Extension - Monitor refresh and change of tab