If you have previously disabled Flash in the past, you may have enabled it for these sites.
The site may also be requesting Flash because it is required.

If you want to stop Flash content from loading, try this Firefox add-on:
Flashblock

I believe Flash is disabled globally; however, it might make sense that if a website requests it, it still loads even though it doesn't actually function once loaded (on Flash content I get a message that Flash is disabled). I assumed if it were blocked it wouldn't load at all. Just a minor annoyance. I will try Flashblock and see. Thank you.

If Flash is set to "Never Activate" then Firefox should not allow any site to use it. However, I believe it may be possible to create site-specific exceptions. Tracking down the site which is running flash may be tricky due to the amount of third party content on Facebook (Facebook itself uses at least 3 different domains, then there are ads, embedded games, etc.)...

There are some technologies which might allow sites to bypass Firefox's normal use of plugins and instantiate the Flash ActiveX control used in IE.

What is the name of the process you see in the Task Manager?

To prevent Firefox from running Flash outside of plugin-container.exe, which should prevent Flash from having its own entry on the Processes tab, you can disable the Protected Mode of the plugin. Then if you see Flash running, it would be due to another add-on (e.g., plugin that hosts ActiveX controls), or another browser or application.

This support article from Adobe has the steps to disable Protected Mode under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

Do you see a grayed plugin button on the location bar indicating that the Flash plugin is allowed?

Does the "Flash Is Disabled" message disable on Flash content?

Flash content is grayed out and has message "Activate Adobe Flash." Plugin button on location bar also indicates Flash is blocked. When Flash loads I see two instances of "Flashplayerplugin_11_9_900_117.exe" in task manager. To me this suggests the content is blocked but Firefox or other program is fetching Flash anyway, as jscher2000 mentioned. The delay caused is irritating but sounds like I would waste even more time trying to find a fix. Another site I notice this happens on is Yahoo mail.

Seeing the Flashplayerplugin_*.exe entries in the Task Manager generally indicates that the Flash Player's protected mode is active. Otherwise, all Flash content played by Firefox would stay inside plugin-container.exe. I don't know whether disabling protected mode would help with the sluggishness, but since it can resolve some other issues, you may want to try it.

See this support article from Adobe under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?