It’s nice to see an example of clear, personalised, instructions. I just upgraded to Ubuntu (I’ll post about it later), and visited the Firefox site to pick up extensions. It gives me the following message:

Firefox on Ubuntu

You appear to be using the Firefox package provided by Ubuntu Linux. Ubuntu distributed a new version of Firefox which contains the security fixes from Firefox 1.0.4, however, they did not update the version number, so we have no way to tell whether your copy of Firefox contains the security fixes or not. A request to Ubuntu to update the version number has been filed at Ubuntu Bug 10681. A workaround you can use to get access to addons.mozilla.org is given in comment 3 on that bug. Please ensure you have updated to the latest Firefox package using apt-get, Synaptic, or the Ubuntu Update Manager before trying the workaround.

It’s nice that not only is the message specific to this browser version and platform, but it’s lucid about the problem that’s occurred and what I can do about it. Perhaps it would be nicer if the presentation was a bit more structured - e.g. as bullet points - but the information is all there.