Last time I restarted my Firefox I noticed something untypical and strange. The last automatic update of the browser to version 34.0.5 was 9. DEC. From that time (after the update) I probably didn't restart Firefox or maybe I did it only once because I can remember a hint about tracking which I saw for the first time. Anyway, recently I had to close the browser (done correctly) and when in few hours I launched it again (no reboot of PC in the meantime) I noticed that there is no the NoScript's button. Moreover it seemed like there is actually no NoScript installed - I checked add-on's list, about:support page and extensions directory - there was even no xpi file of the add-on inside. I checked my backup of files from the day before and the file of NoScript was situated in the extensions directory. Moreover I have a screenshot got the same day in which the button is seen yet. I copied the backed up xpi file into extensions directory and after the next restart Firefox asked me about installation of add-on from file which was found so I've got my NoScript back, but in fact when I launched Firefox the first or second time after update the NoScript disappeared. How can it be possible? What would happened? Are there any similar cases reported and known or is this a kind of explainable bug? I mark that I've got always a lot of tabs opened, but there was no such a problems before. And surely I'm aware that Firefox can check the add-ons and disable some of them during update process but in my case the add-on was completely removed without any warnings. The rest of few (most popular) add-ons I've got survived ;). Firefox version is 34.0.5. NoScript version is 2.6.9.6. The system is Windows Vista.