I've just posted a new version of Duplicate Tab to WTS, and I feel I need to give an explanation to certain new strings.
The strings used for this warning are (located in duplicatetab.properties):
duplicatetab.invalid-url.warning = The hyperlink contains an invalid URL, and can not be opened in a duplicate tab.
duplicatetab.invalid-url.solution = Duplicate the tab anyway
Secondly I have added an option when merging windows to place popup windows next to their opener as a tab. This option is only available in Firefox 1.5 or in Firefox 1.0.x when the tablib extension is installed.
The string used for this option is:
<!ENTITY duptab.merge.place-popups-nextto-opener.checkbox.label "Place the popups next to their openers.">
All the other new strings are visible in the options dialog, so I think I don't need to explain these.