How can you set the DEFAULT to "Allow Data Storage ONLY for the Session" and CHOOSE sites to allow data storage?

I think that would be done by setting clearing site data on shutdown, and only exempting the few sites from that sanitization?

. Thank you so much for replying jbr. It's so kind of people to try to help each other out. I think I didn't describe what I'm trying to do, as clearly as I might have.

That's still not setting "Allow only for session" as the DEFAULT, and having to enter ONLY the URLs for sites I wish to "Allow" to leave data in local storage until I remove it (or it expires). This method would still require actions on my part to clear each site's local storage) every time I close it's tab, unless I want to let it stay on my PC until I close the browser.

I don't close my browser all that often - I have a switch installed that cuts off my (cabled) internet connection to my PC until I switch it back on. When I do close out my browser, I have to reset up my email pins, reset up my password manager access, etc.. And as I understand it, some items can be missed, and left forever in your Local Storage, if they aren't "scheduled" for removal at next startup. There is an extension "Auto-clear Site Data" that tries to make up for Firefox's oversight, but it doesn't work right for me - I keep having to re-sign in every time a new tab opens, even if I'm opening a new tab from a webpage I'm already signed into, which is (maybe) worse than having to manually clear the data every time I close a tab.

For Privacy, "Allow for Session ONLY" should be the DEFAULT, with only the FEW "Allow" exceptions having to be listed. Firefox really should fix this.

What I'm looking for is a way to set "Allow sites to access Local Storage 'ONLY for Session'' as the ''DEFAULT ''' condition for 'ALL sites', EXCEPT for the FEW sites I list in the exclusions, that I want to allow to leave their data in Local Storage. It shouldn't be set up so that the 'majority 'of the sites I visit require special handling every time I close a tab, (either manually clearing that site's data, or taking time to add it to the "exclusions" list as "Allow for Session" - imagine how BIG that list would become! ).

Your suggestion works, of course. I'm just looking for something more user-friendly. I think the Firefox system design is backwards in this instance, and I can't find a way around it. I am hoping someone else has (or will). You should be able to set the action you want 'Most Of The Time' as the DEFAULT, with the FEWER things that require exemption from that DEFAULT, listed as EXCEPTIONS, don't you think?

I will be using your method until either Firefox fixes it, or I find some way around it. There is also an extension "Clear Site Data" I haven't tried yet, but I'm not sure if it deletes EVERYTHING that site put on your harddrive, including sub-sites, or not. There's always Private Browsing, but I'd lose extensions like "Containers" & "OneTab", which are the most important (to me) extensions I have. That delete-ALL-site-data default on closing a site's tabs, feature of Private Browsing should be a BASIC browser feature IMHO. .

"Allow for session" means a) until shutdown, and only b) when you don't use "restore session" functionality, automatically by reopening tabs on startup, or manually by restoring a window from history.

(I'm calling this out specifically as otherwise what you were asking would be exactly accomplished by the other setting combination I mentioned — it just seems your current setup does not really do what you expect it to.)

So you might want to look for a different strategy, according to your description.

There are addons that "clean up" storages after visited sites, after certain period of time — e.g. if you don't come back in 15mins, the data storages get sanitized.

Just for context "clear on shutdown" and private browsing while potentially appearing as similar in results, are vastly different in the principal design — private browsing never persist anything to disk, and only ever keeps the backing session in memory. So it "fails shut", e.g. in case of power outage. Whereas clearing data on shutdown is a "nice to have" over otherwise normally stored quota, to primarily have storages safely written on disk, and then sanitized on shutdown or after restart — however in cases of crashes or power failures, i.e. not user–initiated shutdowns, where the sanitization could only be implied as deliberate, the data is expected to "fail open" — i.e. give users chance to finish their transactions etc. after unexpected events if need be (and only sanitize on the subsequent shutdown).

Your use–case makes sense, but the decline in the addon reliability basically underscores the complexity of the issue at hand — basically breaking the web platform standards contract underneath the (potentially running) sites; or if they have service workers active exclude them (which might appear as defective to end users not being able to "see" the reason for that), so the only "safe" way is to clear on exit, when all the processes get spun down and sites won't be able to re–write their storages at that point. (That's probably why it has always been an addon territory, and why it always was this flaky.)