If you want a clean start, you can create a new profile: Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. Click the "Create a New Profile" button, then click Next. Assign a name like August2023, ignore the option to relocate the profile folder, and click the Finish button. Scroll down to August2023 and click its '''Launch profile in new browser''' button. Firefox should open a new window that looks like a brand new, uncustomized installation. '''Please do not connect this new profile to your Firefox Account right away! That will Sync over the unwanted data.''' ''Firefox will use the August2023 profile going forward, but you can use the about:profiles page to launch other profiles if needed.'' If you had connected your current profile to your Firefox Account, and you want to be able to use it in the new profile eventually, then we need to figure out how to clean out the data that's in there. Do you want to flush everything, or only certain types of data?