Can you elaborate on your inline tab history. I use Google Reader and
I'm not sure what you're referring to. Is this like bread crumbs?

But I definitely think the history can be improved. For instance,
currently in Firefox, "show all history" just lists the sites you have
visited. Wouldn't it be much more useful if the history was shown in a
tree like diagram that tells you that Site A led you to Site B and
etc?

Regarding the ubiquity part, I don't think I understand the purpose of
using ubiquity in a web browser. For a really complicated software
like Word with hundreds of features, ubiquity could help you search
for a feature. However, in Firefox, there are relatively few features
and (as shown in usage heat map) even fewer ones that people use
often. (Especially with Firefox 4, they are grouped much more
logically and with more commonly used features displayed more
prominently). So wouldn't users prefer to click twice or three times
to access that feature through the menu system rather than type
commands into ubiquity (since it's less effort)?

Would you have to type commands copy and paste to perform these
actions (this might get tedious), since the Human Interface does say
that there should be only one way to do things. And how would you
introduce users to other commands (besides Browse) such as private
browsing session, or save page, or open file, or undo closed tab (for
example)?