Bewertet mit 5 von 5 Sternen
For the fans of this theme, which was not updated so as to include the new changes in design, there are not too many options. First, download the theme by right-clicking 'Save link as', then modify extension to zip, unzip and edit install.rdf file so that the line on the max version says something like 1000... as stated in previous comment.
Then zip all the contents of the theme and change the zip extension to xpi. Now, when installing from file, the toolbar will still not look good. A solution would be to install the Classic Theme Restorer addon and then remove all the toolbar items that look wrong (that have not been updated). Luckily, some buttons still look fine, like the downloads button or the fullscreen button.
Another solution for the captive fans of this theme to have it on an up-to-date browser is to install it (after the aforementioned change) in Pale Moon, a browser based on Firefox (but that didn't follow the latest design changes).
Keep the modified xpi file at hand in order to use it after updates, as specified in previous comments.