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.)

Thank you so much, jbr, for taking your time to give me such a comprehensive reply. I'm so happy to find an intelligent mind to pick. The online explananations don't always make complete sense, or they are sometimes ambiguous to me.

I do have a battery backup, so I have time to properly shut down in case of power failure, but the effects of a crash are unpredictable. If I have doubts, I generally restore last Sunday's backup (Macrium Reflect). My data is on a separate drive and backed up differently (with cherry-picked items from my system drive to re-restore OVER a system restore). BitWarden stores my password data on their servers. I rarely have a crash, but it can be a problem when it happens. Doesn't really matter, tho, what I might do - most people are probably not as paranoid as me.

(a.) If I used Private Browsing (Firefox) I can't use Containers, but wouldn't Containers be redundant in Private Browsing, since nothing is written to need clearing? (Private Browsing WILL write to OneTab, it just won't display it there, but I could run it in another (standard) window. (b.) Is there anything I need to be aware of, if I just use Private Browsing? Any downside? How does PB keep from breaking sites (i.e. fool the site into thinking it is writing cookies)?

I'm less concerned about cookies, than I am about the potential for a site storing huge amounts of their data on my drive in Local Storage indefinitely. THAT's what I want to prevent. (c.) Do you know of any "Clear Data" extension, or Firefox function, that clears everything in Local Storage (and allows you to exclude certain sites data from being cleared)?

If you are feeling extra-generous today: (d.) I don't really understand how Service Workers function, and why you would want (or not want) to clear them when you leave a site/close it's tab. (e.) Would PB take care of this on it's own?

And when you manually "clear" a site's storage, does that include its sub-sites?

(f) If you set Firefox up to clear on closure and check every item, does it clear everything (including things like Service Workers? And leave in storage anything stored by exempted sites? Is PB still better? Well, no way to exempt sites from being prevented from saving data, I guess. Ugh, it's so confusing.

jbr: "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. Anne: I thought "Allow for Session" meant for that SITE's session; I didn't realize it meant until you close the browser; you're right, it wasn't doing what I expected, so thanks. (I don't use "restore session" or "reopen tabs" or restore a window from history.) jbr: 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. Anne: Is there one that you can manually activate just before you close a particular tab that will act on that particular tab site only (that would wait until it's last tab/sub-site was closed)? Does EVERYTHING that was saved get sanitized/removed? Or would Private Browsing be better for that (especially Local Storage, where space and time held aren't as limited as they are for cookies). What about Service Workers? My brain hurts. I need time to digest all this. It really IS complicated, isn't it?

I think most of available content online only describes the surface, or cargo–cults the "popular" facts without actually understanding the underpinnings — which is oftentimes prerequisite to intentionally make the choices for one's workflows. So once you're outside of the usual universal advice, it gets very specific, based on the needs.

Session cookies: The long read is developer.mozilla.org/docs/Web/HTTP/Guides/Cookies#removal_defining_the_lifetime_of_a_cookie — specs says "browser decides", and it's customary at the shutdown.

Service Workers: They are part of site permissions, not site data IIUC, so to really clean out everything even potentially written afterwards by a running worker, yes you'd need to manually unregister it. Honestly I'm not familiar with an addon that I'd rely with my data on — so yes, I do use private browsing for these purposes. (I won't even try to touch how workers operate, if you glance the intro developer.mozilla.org/docs/Web/API/Service_Worker_API/Using_Service_Workers you'll see that any working knowledge for casual data sanitization implications probably means having to understand all the tech on the worker part, and then all the sanitizer, origin and permission logic in browsers. Somebody might be capable of explaining that in simple terms… I'm not;D)

Private browsing: The sites are not fooled, as long as the tab is running, they have the equally looking storage APIs available to them. They are not aware they are being limited in a way. It's just kept in memory for the current session, and never written out, so once closed, it disappears. Private browsing might have a slightly elevated anti–tracking settings, so it's possible the sites are allowed less things per se in that mode, but I see that as a benefit. (Yes, workers are unregistered after closing the private windows … similarly to any granted permissions, like locations, peripherals and similar, that I also like not to persist.)

If you're mostly concerned about data crud the sites leave behind, I'd leave that to the browser to handle. Its quota manager is designed to prune that data, so it's not like you'll have the persistent storages forever — and if you positively do not want sites to keep that stuff around, the clear on shutdown functionality, with data type granularity and exclusions to manage, is probably the simplest way to strip sites of their storages periodically.

One note here is people expect "never remember history" mode to be cleaning up stuff but it's only not saving new things, which is different. So I'd actually advice not using that permanently–private mode, but have a normal browsing mode enabled, having some shutdown sanitizer rules, and then on top of that be using private windows for things that you want to nuke faster.

Two toolbar icons you might find interesting to learn about and embrace: 1.) private windows have a "fire" icon to wipe the private session completely, close out tabs, remove their backing sessions, and give you a clean slate of just the private browsing mode content, without having to close out and hunt down the tabs and windows manually. And also 2.) normal browsing has a "forget" icon that you can place on the toolbar (from its "Customize" context menu) that has similar functionality for normal browsing mode (word of caution here as well: it also closes open tabs, so it might not be what you're looking for… just naming some less utilized tools that might come handy depending on one's workflow.)