Hi, do you want to delete particular sites, or ranges of dates, or everything? You can find some info in the following article as a starting point, but let us know whether that covers it or you have additional questions.

Delete browsing, search and download history on Firefox

Note: Please be careful in the dialogs that have a lot of checkboxes if you do not want to remove cookies (which would log you out of sites you might currently be using).

In case you use "Clear history when Firefox closes" or otherwise clear history:

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exceptions for passwords and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an allow exception you may want to keep