How to get rid of DivX Plus?

I trialled DivX Plus many months ago and didn't like it, so uninstalled.

But now every time I open Firefox, I get a message telling me DivX Plus installer is trying to access the internet (denying access only lasts for one session), or if I'm not connected it tells me that DivX Plus installer needs to be connected to the internet to install.

But I don't want to install DivX Plus, do I? So why does it keep telling me I do?

I've searched my computer and there are no files with 'DivX' in the name, so can anyone tell me a file name to look for which I can delete and stop this happening?

Thanks

Wow, what a spammy wasteland

Wow, what a spammy wasteland of a forum. No wonder I'm having trouble with your software.