Hi Ron, you can download a full installer, then remove the existing program folder (typically C:\Program Files\Mozilla Firefox), then custom install on D drive. ([[Custom installation of Firefox on Windows]]) However, that might not have much effect because it does not move your data folders, and the disk activity you see probably relates to data folders. As a test, and assuming you have a high speed connection, you could completely disable caching of web content to disk and see how much effect that has. Here's how: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''browser.cache.disk.enable''' and pause while the list is filtered (3) Double-click the preference to switch the value from true to false If that has a noticeable effect, I think there is still a way to set Firefox to use a custom folder on D drive for your cache. (Need to research that to remind myself of the steps.)