Firefox will create a large cache if your hard drive or SSD has a lot of space. To constrain it:
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
(2) In the search box above the list, type or paste cache.d and pause while the list is filtered
(3) Double-click the browser.cache.disk.smart_size.enabled preference to switch the value from true to false -- this is necessary to override the size, otherwise Firefox will enlarge it again in a day or two
(4) Double-click the browser.cache.disk.capacity preference to display a dialog where you can edit the size, then click OK -- if this number is 7 digits, for example, 1000000, that is 1 gigabyte; if this number is 6 digits, for example, 500000, that is 500 megabytes.
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
(2) In the search box above the list, type or paste cache.d and pause while the list is filtered
(3) Double-click the browser.cache.disk.smart_size.enabled preference to switch the value from true to false -- this is necessary to override the size, otherwise Firefox will enlarge it again in a day or two
(4) Double-click the browser.cache.disk.capacity preference to display a dialog where you can edit the size, then click OK -- if this number is 7 digits, for example, 1000000, that is 1 gigabyte; if this number is 6 digits, for example, 500000, that is 500 megabytes.