With Firefox 70 you get the new privacy dashboard which will provide you will statics on how many trackers etc. Firefox already blocked.
You might want to get up and set your tracking protection settings fully strict.
Hint: I can't remember a page that those settings broke. Along with this I also run "µblock Origin", but you might want to start slow and just setup Firefox properly :)
@sheogorath the instapaper browser extension will break if you set to block all third party cookies.
That was the only thing I witnessed breaking using this setting.
@puresick After checking my exemptions there also seem to be portal.azure.com which seems to break without third-party cookies.
Haven't been there for quite a while.
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