Flash-Aid 2.2.3 is another plug in checker. I have no involvement, just a satisfied user.
Flash-Aid Remove conflicting flash plugins from Ubuntu/Debian Linux systems, install the appropriate version according to system architecture and apply some tweaks to improve performance and fix common issues.
Download from the Firefox Add-Ons page. Lubuntu 12.04 & Firefox 13.0.1 here FWIW.