Hi kasto,
unfortunately this report is not very useful because it does not describe the problem well. If you have time and can still reproduce the problem, please read https://www.mediawiki.org/wiki/How_to_report_a_bug and add a more useful description to this report. Which MediaWiki version do you use; is there any output in the browser's Error Console; screen shot also welcome.

(In reply to comment #1)
Sounds very clear to me...

ka wrote:

(In reply to comment #1)

unfortunately this report is not very useful because it does not describe the
problem well ... Which MediaWiki version do you use; is there any
output in the browser's Error Console; screen shot also welcome.

The extension "LastModified" is supposed to provide an an in-text message "Last Modified". This bug report is about the fact that "Last Modified" does not show up on some skins (e.g. Classic, Modern, Nostalgia)

There is no error in the Firefox V.23 console and no error in the Apache logs. These are the versions used:

MediaWiki 1.21.2
PHP 5.3.17 (apache2handler)
MySQL 5.5.32

The symptom of this bug is that the "Last Modified" message does not show up anywhere on the webpage. That is, the webpage looks identical with and without the enabled extension. I you still find it helpful to get a screenshot of the empty screen area in question, please feel free to ask again.

Doing some additional research I found in the meantime that with the default "Modern" skin the "Last Modified" message is indeed being sent to the upper right screen corner but it is invisible because it is rendered with dark blue text on the dark blue background.

Hope this helps.

Change 106878 had a related patch set uploaded by Hydriz:
(bug 54450) Fix compatibility with all skins

https://gerrit.wikimedia.org/r/106878

Change 106878 had a related patch set uploaded by Hydriz:
Fix compatibility with all skins

https://gerrit.wikimedia.org/r/106878

Change 106878 merged by jenkins-bot:
Fix compatibility with all skins

https://gerrit.wikimedia.org/r/106878