¶ Settings
¶ Disable Privacy-Preserving Attribution
Opt-out crap pushed by Mozilla 
, can be disabled in settings.
Or change dom.private-attribution.submission.enabled to false.
¶ Extensions
A set of extensions to improve browsing.
¶ Ad blocking
Best solution is uBlock Origin.
Check extension preferences (about:addons) and select your filter list.
¶ Consent-O-Matic
Add-ons for automatic refusal of consent pop-up.
¶ Cookies
Cookie AutoDelete allow cleanup cookie when you close a tab, support whitelisting.
¶ Containers
Containers allow to use different session (Cookies, local storage) for different tab. You can then have two separate session open for the same website.
¶ Multi account container
The feature is present by default but you need to add the Multi Account Container extension to fully use it.
¶ Temporary containers
Temporary containers allow to create temp container to isolate browsing.
¶ Sticky containers
Sticky containers: new tabs and windows will have the same container as the current tab. Links opened from external programs will also try to keep the same container as the tab which had focus.
¶ Tab groups
Simple Tab Groups allow to create, modify, and quickly change tab groups.
¶ Filter search results
uBlacklist allow to filter results from Google, Bing, Brave, DuckDuckGo, Ecosia, Qwant, Searx, Startpage, Yahoo! JAPAN and Yandex.
¶ About:config
One of the best features of FF, allow to change settings which are not always exposed.
¶ Disabling Pocket
Switch extensions.pocket.enabled to false 
.
¶ Add specific domain as SecureContext
Create dom.securecontext.allowlist as a String of comma separated values.
¶ Fullscreen video limited to window size
Change full-screen-api.ignore-widgets to true.