When I open several pages, without starting videos on those pages, Youtube makes background connections (shown in iftop as 74.125.105.x:80 and 173.194.5.x:80 primarily [Google]) that saturate my download link ~800 KiB/s.
If I then try to view any of the videos they will download very slowly and usually stop at either 1/10th or 2/10th's and refuse to continue buffering. If the videos do happen to continue then they will drop to low quality, being visibly pixelated.
None of the pages will display the videos on them yet the background downloading appears to continue without stopping until the browser is closed completely.
When I close the pages with Youtube embeds the downloading continues. To recapitulate - there are no open tabs with Youtube videos but iftop shows many connections and those connections are saturating the download link and preventing direct interactions (eg loading a page in the foreground tab).
The problem doesn't appear to happen when I watch an individual video through YouTube pages themselves.
What's going on and how can I stop YT from swamping my connection (which is presumably just because there happens to be an embed on the page I'm reading).
Ubuntu 13.04, KDE 4.10, Firefox 24, Flash 11