Browser/OS detection is no solution. Then we're back to designing web sites for each browser individually like it has been the practice over 5 years back.
Funny seeing that here. I think these type of Pagepeel-ads have become famous since the german "AK Vorratsdatenspeicherung" used it to sensitize the german-speaking population about the upcoming laws on storage of communication data. They used a
CSS-solution to put it in the top right corner (click for demo) and made Wiki sites explaining how to put it on your own site:
http://wiki.vorratsdatenspeicherung.de/Online-Demo
http://wiki.helge.at/Einbauanleitung (austrian version which adapted the concept)
This lead to a boom of these page peels over all the german-centered web sites.
There is no real Flash support for Linux. The only thing that's there is an outdated flash plugin which is proven to be buggy and leading to the most browser crashes. The only flash plugins that are supported by Adobe are for Windows/Mac, I think.