Rated 3 out of 5 stars

Still works fine, will not install on FF43 due to signing requirement. Easier icon fix from what I reviewed ages ago:

Download extension to desktop
Open in a suitable programme
Go to folder "\chrome\duplicatethistab.jar\skin\icons\" within archive
Extract icon-large.jpg file to desktop
Rename as icon.png
Place this file into root folder of archive (the one that's got install.rdf file in it)
Install to Firefox.
Should now have an icon under add-ons menu

Rated 3 out of 5 stars

In addition to what I typed below, to get an icon to show up in firefox 4 & 5

Once extension downloaded to desktop, open .xpi file
Go to folder “chrome\duplicatethistab.jar\skin\modern\duplicatethistab\”
Extract file labelled "tab-drag-duplicate-indicator.png"
Edit in a suitable programme that can resize by pixels
Resize image to 48x48 pixel, & save as Icon.png
Resize ORIGINAL file to 64x64, & save as Icon64.png
Merge back into .xpi file & drag into firefox to install
Sourced with help from http://blog.mozilla.com/addons/2010/12/02/toolbar-buttons-in-firefox-4/

This review is for a previous version of the add-on (1.2.1-signed.1-signed). 

Rated 3 out of 5 stars

For Duplicate this tab:
One thing that's missing from this port over is an icon for the add-ons screen (even a default icon of a jigsaw piece)

By removing the following line from the install.rdf the default icon shows up under 3.6
<em:iconURL>chrome://duplicatethistab/skin/icons/duplicatethistab-icon-small.jpg</em:iconURL>
Note Firefox 4.0b10 still has no icon shown. The file referenced above does exist at the above location though.

This review is for a previous version of the add-on (1.1). 

Rated 3 out of 5 stars

From Duplicate tab there is a jigsaw piece that shows up in duplicate tab extension under Firefox 3.6. If you install duplicate tab extension into Firefox 4 beta 10 at time of typing this (needs a max version hack to get it to install), the jigsaw piece shows up.Contd.

This review is for a previous version of the add-on (1.1).