Firefox has been acting up on my laptop for the last few months. Finally, I decided to find a solution to my problem and saw that resetting Firefox might solve this problem. Well, it did solve my problem and finally Firefox doesn't freeze up anymore. But now I cannot re-download Xkit, my extension for Tumblr which is much needed. Xkit was working perfectly before I reset Firefox, but now I only receive the attached message when trying to re-install the extension. I've tried uninstalling Firefox [and all previous data and settings] but still nothing.