I'm suddenly getting pop-ups for various sites (usually with a table of ebay or amazon items). They often appear when I click to type in a box on a site (e.g. in a search engine), but it happens randomly on any site and the window it opens always has a different address even if it is displaying a similar page. This started when I still had the older version of Firefox so I thought maybe updating it would help, but it is still continuing with the latest version. I have block-ups blocked.
NoScript (Follow the directions for training the extension to only run scripts on sites you want. If there are sites you use that have annoying behaviors, turn off their ability to run scripts until you go use the site, then turn them off again when you leave. )