Running flash in Firefox under Linux never worked all that well for me. npviewer.bin would often start taking 100% of the CPU, or lock up and stop displaying video.
I also don't understand why someone would be unwilling to install a proprietary browser, but willing to install an (unsandboxed) proprietary plugin.
I feel bad that Firefox will become less popular as a result of this decision, but Linux users who are willing to install Chrome will probably actually have a better experience than in the past.
P.S. I don't have flash installed and haven't for the last few years. I don't miss it.