There's more discussion in this file between Howard Trickey (who refers to himself as an "erstwhile fool", having written Charon for Inferno), Duff and other Plan 9 enthusiasts.
The displayed level of knowledge and engagement with the requirements for building a web browser isn't exactly off the charts. I think it's fair to say that Duff didn't have a lot of patience with the project. He saw it as a moving target that probably couldn't ever be hit. For Plan 9 the classic web browser is a culturally alien type of software: complex and to some degree necessarily monolithic.
Here's what Duff said:
> how come mothra bit the dust?
I wrote it. It was not in good condition when I left
Bell Labs. Understantably, nobody else wanted anything
to do with it, so it died.
Its biggest shortcoming (other than its general
internal hidousness) was that its document imaging
model was fixed before <table> entered the picture.
Deep down it believed that documents were running text
with embedded line-breaks and indent changes, meaning
there's no good way to get tables or frames to work.
Also, if your browser doesn't closely match Netscape
and Microsoft, people will believe that it just doesn't
work, regardless of how good a job you do of meeting the
published specifications.
On the other hand, I still think its idea of how to handle
navigation (mostly the panel with an LRU list of pages
visited) was better than anything else I've seen.
Writing a web browser is a fool's errand. The
specification was changing faster than I could type, and
still is.
And here's Rob Pike:
> Surely somebody must be trying to port Mozilla to Plan 9?
While that would be better than no browser at all, Mozilla
is just the sort of stand-alone monolith that we're trying
to argue against. And of course, everyone else in the
world is trying to turn their system into a giant web
browser. I'd rather see web access be one aspect of a
system in which the pieces work in concert.
-rob
I think most people who've given the web browser platform any serious thought would agree that the way Duff and Pike are talking is indicative of not really having taken the problem seriously. The discussion continues in that speculative vein.
They had the luxury of being able to choose (effectively) to reject the web user experience and they took that option. Tom Duff probably wouldn't claim that he was speaking about the intricacies of web browser development with great authority!
There's more discussion in the 9fans archive. And see also Abaco, another attempt at a graphical browser for Plan 9: http://lab-fgb.com/abaco/
Well, he wrote a browser for Plan9 (Mothra), so if he said that, it's not for lack of experience.