Egads... Rated 2 out of 5 stars
This add-on, while requiring some very clever work on the part of its creator, suffers from two very serious problems.
First and foremost, the attractiveness of this add-on stems from its ability to upload themes to a Wordpress blog without the hassle of using FTP. Or so you'd think.
Most first-time Wordpress users undoubtedly have struggled with trying to figure out how to upload "unofficial" Wordpress themes (i.e., themes written by third parties that are not directly available through the Wordpress.com infrastructure), only to finally give up and resign themselves to using one of the relatively few (and relatively bland) themes made officially available through Wordpress. The reason for this resignation (and disappointment) is simple: To upload a "third party" theme to your Wordpress blog requires the use of FTP. The problem, however, is that if you're like the overewhelming majority of Wordpress bloggers, your blog is hosted by Wordpress, not another server, and Wordpress does not allow FTP on Wordpress-hosted blogs. So concequently, the Oneclick Installer leaves us with a catch-22-esque problem, in that it would seem to offer hope to those ~95% of Wordpress bloggers who can't use FTP, but in order to install the add-on, one needs to first upload it to his or her Wordpess account... via FTP.
While it is true that the assumption that this add-on will solve all the problems of non-FTP users is really only a misunderstanding on their part, the author of this add-on should really have made this rather important tidbit of information a little more obvious. Which brings me to my second point...
The installation and usage instructions that accompany this add-on (both on this Mozilla download page and the author's personal page) are so poorly written that it perhaps demonstrates that one's skill with writing code is inversely related to one's skill with writing lucid, complete sentences. An upfront disclaimer about this add-on not working for those without host-FTP access would be a significant improvement.
If your blog is hosted by someone other than Wordpress, this tool is probably great, and I'm envious of you. But for the 95% of us that I mentioned above, it's more like a gradual, curse-riddled, 90-minute let down resulting in defeat.