Fix your Sources
If you are seeing the “The update information is outdated.” warning, you should use the
Software Updater to check for updates, and install any available. That should get rid of that warning, unless one of the sources you've added is unavailable or unverifiable. In that instance, you should remove the affected sources.
Flash is Dead
Since Flash is deprecated in Firefox and on Linux, I think it is safe to assume that regardless of whether it is a numbering issue or not, an official fix is not forthcoming. If you can, try to simply get by without it, or you can right click to allow always.
Gnash is a GNU alternative to Flash. It does not appear to be actively maintained.
LightSpark is another alternative, but one which appears to be reasonably well maintained.