Please note that these 2 issues are different than eachother:
1- Yes there is a problem with firefox/mozilla browsers. When you click karmabox, it opens under the post layer (as in the screenshot above) and not allows you to use it properly. We are addressing this and it will be fixed soon. For now using IE will help as it does not have such problem.
2- The problem I tried to help in this thread was balboa29's inability to give karma for any posts due to system's giving an error message. We shouldn't have such a problem and if you get an error message when trying to give karma which you shouldn't have, please let me know.
Obviously you'll get "you can't give karma same post twice" error if you try to give karma to the same post twice but if you are getting such an error even if you didn't give karma to that post before, please report here and make a test with my post above.