Firefox alerted me that a critical update was available:

Yes, this is a indicator of a critical update. Of course. (Don’t miss the heavy dose of sarcasm there!) A red button like thing with an up arrow … or something. Personally I would spell it out in a little more if it’s that important. There’s plenty of space available in the average Firefox installation window. [Critical Update Available. More…]

I started to go through the process and got to here:

(click image for larger size)

Firefox encountered problems when updating your software, and as a result not all components could be updated.

For extra pain, I clicked details. I am particularly fond of the details that get truncated so that the actual detail isn’t available: “Not a valid i…”. The dialog isn’t resizable in case you were wondering.

How did I fix the problem? I clicked the [< Back] button, and Firefox started the download. Go figure.

What should the software developer do in this case? Again, I’d suggest giving the user appropriate behaviors when this occurs. Retry. Cancel, Send Error, Support Forums, etc. If the users chooses to see the details, make it possible to actually see the details and copy them into an e-mail or to submit them to a bug clearing house minimally.