Should only be 350MB as your Cache unless something has changed that. Have you looked under Tools - -> Options - -> Advanced - -> Network and under the Cached Web Content there should be no tick mark and should be greyed out 350MB Firefox should be using the default which is above 350MB If you are getting more it should say how much you are using. If so you can put a check mark in over ride and set it to 350MB Restart Firefox and keep a eye on it. Now if you are talking Temp Files that has not a lot to do with Firefox but a lot of how Windows is set up or what programs use the Temp Folder. Think you would need to start here and have a look around : https://www.google.ca/search?q=how+to+limit+Temp+Files+in+Windows&ie=utf-8&oe=utf-8&gws_rd=cr&ei=zxpnWeq9Mc3YjwOBirewDA Possible to find what programs are using that, try here : https://www.howtogeek.com/225073/how-to-use-windows-10s-storage-settings-to-manage-your-hard-drives-free-space/ If not using MS Disk Cleanup then there would be lots and especially after a windows update as you have to run the program then click Clean Up System Files and there can be multi gigs in that. Try checking this for titles and also change to windows 7 to see if get something https://www.google.ca/search?q=how+to+limit+Temp+Files+in+Windows+10+how+to+geeks+&ie=utf-8&oe=utf-8&gws_rd=cr&ei=dRtnWYHzD4rMjwP6072wBQ Also would be a good idea to check for malware : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Please let us know if this solved your issue or if need further assistance.