I've tried the following, and to no avail on the standard-issue Desktop
CD-installed Xubuntu 8.04 desktop OS

1. dumping/purging all FLASH-related plugins, helpers, including Adobe's and
GNASH.

2. tried looking (in synaptic) for restricted codes AND flash, but the search
process just simply shows "adobe plugin nonfree" or something like that.
Which when installed, does jack sh*t.

3. A few sites recommended getting the plugin from adobe site, so I did.

--and now in my "Add-ons" menu there are 2 Shockwave helpers, where you can now
"enable/disable" on or both- (try using the newest one, flash doesn't work,
older one works but this / was/ will be the problematic crashy-pants one).

Firefox performance is just crap - bordering on super-unstable on youtube, but
on my personal site, I have movies made with flash 5 so it works fine. I think
perhaps the latest plugin (from Adobe, or from the repository) simply isn't up
to the task just yet.

When the plugin does `work`, the LARGE grey triangles are Annoying!
They would be somewhat tolerable if they went away instantly after clicking on
them,
but due to the performance issues, they don't. Oh well.. boo-hoo.

I am contemplating purging Firefox (won't lose bookmarks as I use Foxmarks).
Then I'll reinstall Firefox 3.x.

And if i really really really need to bother myself with the SUPERB
entertainment of Youtube et al,
then I'll simply use another browser.
Perhaps my luck will be better with Konqueror, or even Midori