how to save a pic with right mouse button in X_treme theme?

I use the x_treme theme and there I can not do a "save as" with the right mouse button (full image popup). E.g. with Carbon it workes.

How can I change that?

Gallery version = 2.3 core 1.3.0
API = Core 7.54, Module 3.9, Theme 2.6, Embed 1.5
PHP version = 5.2.6 apache2handler
Webserver = Apache/2.2
Database = mysqli 5.0.32-Debian_7etch8-log, lock.system=flock
Toolkits = ArchiveUpload, Exif, Gd, SquareThumb
Acceleration = partial/900, none/0
Operating system = Linux wp171 2.6.22.19-he-xeon-64gb+2 #1 SMP Tue Sep 2 14:02:52 CEST 2008 i686
Default theme = x_treme
gettext = enabled
Locale = de_DE
Browser = Mozilla/5.0 (X11; U; Linux i686; de; rv:1.9.0.5) Gecko/2008121621 Ubuntu/8.04 (hardy) Firefox/3.0.5