Add-on Install problem

[Sheddie]

I decided to persevere. I retract the comments I made in my last post re Ubuntu not working. I found that when I came back to give it another go\ everything worked fine Including the wireless broadband. In fact the connection to my ISP was completely automatic. Unlike the Windows process where I have to launch the connection manager.
However, I'm having a problem installing the Firefox Add-on AdBlock Plus. I downloaded it and when I clicked install I got a popup telling me that Firefox has prevented Adblock Plus from asking to be installed - not a valid file type. Can anyone help with this.
Thanks
Mike:guitar:
PS: I think I might end up dumping windows (hope I can get Linux versions of my Family History Software (Brothers Keeper).

[quixote]

Firefox has preferences to block popups and warn about software that tries to install. The latter should only be warning, not stopping it, but those are the two things I would check. The first one is under Edit > Preferences > Content, Block popups. The second is under Edit > Prefs > Security.