Alfs Buttons от Pante

This extension its a little "companion" for the userChrome script "Alfs". It just adds a button with the URL of valid sites (YouTube and Vimeo at the moment), so in that way the script can detect the link to open the video in the sidebar.
So the result is that it does works as a picture in picture solution with the sidebar.

Note that this extension by itself does nothing more that just add a page action button (in URL bar).
The process its clean and simple: The button itself contains a fixed icon file (as any button like that), but when it appears: the 'path' of the icon get added an extra "?start=" followed by the URL of the video watched (the actual Youtube/Vimeo tab). That icon path then is detected by the script and get the URL to send to the sidebar.

This is a way of communicate between the userscript and the "properties" (the URL) of the tab. Its a workaround for send that tab URL to the userChrome script.

For more info & bugs reports, check the repo: https://github.com/thepante/alfs-firefox
Icons used are from Iconscout.com