Flash player installation problems, hopefully solved

Been having trouble with flash player in Firefox, in my dark
background Windows color scheme. I do Windows backups, so my
system is neat. But for some strange reason, flash player has been
messing up in YouTube, for weeks or longer, through several
installations and restorations (of various things).

My latest attempt to solve the problem... Found a link to the
instant installation page on Adobe's website, and made a shortcut
to it. I grabbed the latest flash player uninstaller. Left open
only one tab in Firefox, a text page, and closed Firefox. Ran the
uninstaller. Opened Firefox and browsed to that Adobe flash player
installation page, to install it. Might have closed Firefox.
Browsed to YouTube, and BOOM everything is correct for a change.

I think that about sums up everything I did. Something that looked
troublesome (before) is the way Firefox handled the flash player
update. I was getting two prompts (the information bar and
another) to install flash player, and then somehow the video was
played anyway, supposedly before flash player was installed. But
the video windows looked very wrong, then and after I accepted the
manual install.