At least it was a small scale experiment and not something that rolled out to the whole install base, I use Firefox on a couple of computers and didn't see it myself. But should you really need user feedback to know that inserting an overlay that looks like in-page ad content is a bad idea?
Two reasons: clueless management who chases short term returns, and a rabid fanbase that will constantly make excuses for them no matter how much they decline, because "at least they're not Google/Microsoft"