Dear all, The problem: I am accessing a webmail server (Outlook) located at a British university. Either when I log in or log out there, Firefox stops responding. I have to close the window and then restore the session to get my tabs back (which has led me to open very few tabs these days). The diagnosis: I thought it might be malware, especially because sometimes tabs opened with the name "prosperent.com/", but were not fully loaded. I think whenever I used CCleaner just before logging in, the log in was smooth. Attempted fixes: - First of all, I reset Firefox internally - to no avail. /// Next, I uninstalled and reinstalled Firefox, but the settings were remembered for some reason. So I uninstalled again, deleted all personal Firefox setting folders and reinstalled it again. Firefox was now pure in start mode - the problem persisted. /// Then, I installed a malware programme to check for hidden viruses in addition to my normal anti-virus programme. The malware programme found a few cookies and deleted - the problem persisted. /// Last, I started Firefox in safe mode, which worked - until I closed the browser and opened it again. The situation still is that with some pages Firefox opens a tab with the URL "prosperent" and crashes when logging in or out the webmail account. Only when I empty the cache, does the problem not occur, but this cannot be the ideal solution to the problem. I do not know what else to do now. I would thus be very happy to know what else you might recommend here. Best wishes, Matt