Change 76105 had a related patch set uploaded by Aklapper:
Add bmo extension InlineHistory

https://gerrit.wikimedia.org/r/76105

This extension has been in use on bugzilla.mozilla.org for two years, see https://bugzilla.mozilla.org/show_bug.cgi?id=668506

Its bug reports have been actively handled:
https://bugzilla.mozilla.org/buglist.cgi?&component=Extensions%3A InlineHistory&product=bugzilla.mozilla.org

https://bugzilla.mozilla.org/show_bug.cgi?id=668506#c20 states that "it _should_ work on other installations, however it's largely untested."
However, the extension is also in use on https://bugzilla.redhat.com .

Furthermore, it creates a setting under userprefs.cgi called

"When viewing a bug, show all bug activity"

which admins can turn on by default for logged-in users on editsettings.cgi.

sumanah wrote:

From https://bugzilla.mozilla.org/show_bug.cgi?id=668506 as an example, the inline history only shows up if you're logged into Bugzilla. Is that the preferred behavior?

Created attachment 13019
Screenshot from Mozilla Bugzilla

Example screenshot from comments on a bug report in bugzilla.mozilla.org.
The parts that are shown by the InlineHistory extension are marked.
Note: This is only shown to users that are logged in.

Attached:

(In reply to comment #4)

From https://bugzilla.mozilla.org/show_bug.cgi?id=668506 as an example, the
inline history only shows up if you're logged into Bugzilla. Is that the
preferred behavior?

There is no setting for this, and one potential reason for not showing InlineHistory to non-logged-in users might be a missing implementation for obfuscating email addresses shown when changing e.g. the assignee of a report.

(In reply to comment #6)

There is no setting for this, and one potential reason for not showing
InlineHistory to non-logged-in users might be a missing implementation for
obfuscating email addresses shown when changing e.g. the assignee of a
report.

When I go to https://bugzilla.wikimedia.org/show_activity.cgi?id=1 logged out I just see the username part of the email address, without the domain. Can't that be done here?

Deployed patch for testing at http://boogs.wmflabs.org/show_bug.cgi?id=2 - log in as horst_horstmann@gmx.net, use the part in front of @ as pass, and comment away.

Looking at it I prefer small CSS tweaks, e.g removing these two lines:

.bz_comment.ih_history {
    padding: 5px 5px 0px 5px
}
.ih_inlinehistory {
    border-top: 1px dotted #C8C8BA;
}

from style.css.

Ah well, changes in comment 8 should be a separate patch after getting (unchanged compared to upstream) https://gerrit.wikimedia.org/r/76105 in, so it's easier to maintain.

Change 76105 merged by Dzahn:
Add bmo extension InlineHistory

https://gerrit.wikimedia.org/r/76105

Change deployed (thanks to dzahn).

To see this in action, go to https://bugzilla.wikimedia.org/userprefs.cgi?tab=settings and set "When viewing a bug, show all bug activity" to "On" (it's "Off" by default).

Now wondering whether to set this to "On" by default for all users under https://bugzilla.wikimedia.org/editsettings.cgi . I will probably do this soon, but I'd like to improve the CSS a bit before.

Change 85978 had a related patch set uploaded by Aklapper:
Indent data added by InlineHistory so it is still easy to skim through normal comments. Followup to Change 76105.

https://gerrit.wikimedia.org/r/85978

Change 85978 merged by Dzahn:
Indent data added by InlineHistory so it is still easy to skim through normal comments. Followup to Change 76105.

https://gerrit.wikimedia.org/r/85978

merged/deployed CSS fix

All code changes are deployed so this is available now (see comment 11).
Only question left is whether to enable this by default.

Marking as FIXED for the time being (and keeping it as an opt-in).

I've announced availability on wikitech-l: http://lists.wikimedia.org/pipermail/wikitech-l/2013-September/072107.html

(In reply to comment #15)

Only question left is whether to enable this by default.

"Inline history" functionality is enabled by default now for every user who is logged into Bugzilla, as per feedback on http://lists.wikimedia.org/pipermail/wikitech-l/2013-October/072413.html