Weird. LeetKey's documentation is nonexistent, and I can't really imagine why it doesn't work for you. Maybe you can try directly editing the about:config results for leetkey? Googling "virtual key codes" should tell you what to insert in the entries, or you can recycle one of the default ones.
Every time I come across one, it annoys me. I have to copy the text, open a new tab to the ROT13 site, paste the text, and click the translate button.
Compare this to something like a collapsable spoiler button-box where you press a button and it expands and expands a box with the appropriate text underneath it. Even making a [spoiler][/spoiler] tag that gave a black background and equally black text would be better than the current ROT13 solution.
Was there actually a reason for doing things this way? If so, why not just include the ROT13 translation in the javascript that'd open and close the textbox? Comments? Criticism?