When does this pop-up appears ?? At Firefox startup ?? When you are browsing a specific site ?? between browsing randomly on different sites ??

at start up and some sites, please help. it is really annoying

Firefox 7 is in Beta phase right now. Maybe its better for you to switch to a more stable version of Firefox 5.0.x

-> Tap ALT key or press F10 to show the Menu Bar

-> go to Help Menu -> select Restart with Add-ons Disabled

Firefox will close then it will open up with just basic Firefox. Now do this:

-> go to View Menu -> Toolbars -> unselect All Unwanted/Incompatible Toolbars

-> go to Tools Menu -> Clear Recent History -> Time range to clear: select "EVERYTHING" -> click Details (small arrow) button -> place Checkmarks on Cookies, Cache -> click Clear Now

-> go to Tools Menu -> Options -> General -> in Startup section click Reset to Default button

-> go to Tools Menu -> Options -> Content -> place Checkmark on Block Pop-up windows -> click Exceptions... -> click Remove All and click Close

-> go to Tools Menu -> Options -> Privacy -> History section -> Firefox will: select "Remember History"

-> go to Tools Menu -> Options -> Security -> place Checkmarks on:

1) Warn me when sites try to install add-ons 2) Block reported attack sites 3) Block reported web forgeries 4) Remember Passwords for sites

-> go to Tools Menu -> Options -> Advanced -> Network -> Offline Storage (Cache): click Clear Now button

-> Click OK on Options window

-> go to Tools Menu -> Add-ons -> Extensions section -> REMOVE All Unwanted/Suspicious/Incompatible Extensions (Add-ons)

-> go to Tools Menu -> Add-ons -> Appearance section -> REMOVE All Unwanted/Suspicious/Incompatible Themes (Persona)

-> Restart Firefox

You can enable your Known & Trustworthy Add-ons and Themes later. Check and tell if its working.