It's been bothering me for years. There are a lot of file types that
are essentially plaintext, but are labeled differently to make the
browser's/mailer's decision easier which program is best to handle
this type of file. For example, text/x-diff.
Now, how hard could it be to include a little checkbox "display in browser" in the file download dialog? I mean, it's text after all. But, apparently, it is quite hard. Yes, that's no display failure, that thing has been suggested at the end of 1999 and the bug report pushed back and forth since then. Stupid morons.
However, there's a nice addon which does just this job.
On a related note, since the last upgrade, opening context or dropdown menus will take Firefox up to 30 seconds sometimes. No heavy CPU or disk usage, the application just freezes.
I hope I'll find some time during the next few weeks to migrate to a saner alternative.