Firefox eats memory even when inactive.
I have check in your FAQs and get one suggestion: "Firefox's memory usage may increase if it's left open for long periods of time." Why? You suggest closing and restarting Firefox, but this is not always convenient. Another suggestion was to use a addin but my version of FF is not compatible (I think I'm up to date FF Quantum 57.0.2)
Wšykne wótegrona (1)
Please : Go to the Firefox 3 Bar Menu --> Help ? --> Troubleshooting Information Page and take a look in the Accessibility section if accessibility is set to "true" there. if yes, go to the Firefox 3 Bar Menu --> Options --> Privacy & Security panel and under Permissions check the setting to Prevent Accessibility Services from accessing your browser.
Monitor in Task Manager. Should stay below 2 gigs. If excessive then do below and monitor and change if need to.
Go the 3 Bar Menu then Options --> General --> Performance and untick everything. change the recommended size lower then see how it runs. Note: 1 = No Multiprocessor = slow again. Try 2 Restart Firefox after making these changes please.
For Extensions/addons/themes and more
Please let us know if this solved your issue or if need further assistance.