I'm saying you should not use for SECURITY tokens which, if leaked, can allow others to impersonate your user. So it doesn't matter it uses 40Gb of cached data. Security is not black or white, it is a full spectrum and despite it would be bad for a hacker to obtain a full chat historory or your list of jira card titles it is still less worrysome that somebody able to impersonate you in those services. Security is an arms race....you need to raise the barrier more and more as attacks get more and more sophisticated. So the "then just don't run extensions" or "just don't use untrusted third party scripts", despite it is something we should do, it is not a justification for lowering the bar of all the other stuff we should be doing.
Regarding the references you ask for, what can I say. localStorage can be accessed by any JavaScript running in the page, even from browser extensions or XSS attacks. I'm pretty sure you will find people more knowledgeable than me here [1] and overal just googling for it you will find a lot of resources about why storing authentication tokens in localStorage is a bad idea
[1] https://security.stackexchange.com/search?q=localstorage+sec...
Slack [0] has entered the chat.
Jira [1] has entered that chat.
I could go on but I don't need to. Many web applications that people use store an unnecessarily obnoxious amount of data locally. I can only imagine how much of that is used just once or possibly even never (like images in settings windows that were never accessed).
[0]: On one instance of Firefox on one computer, app.slack.com has stored 1.9GB. On another instance of Firefox on another computer, app.slack.com has stored about 633KB. On a third instance of Firefox on yet another computer, app.slack.com has stored about 600MB.
[1]: Jira doesn't load _at all_ if you've got any secure settings enabled (like... no CORS and no cross-domain cookies and no cross-domain XHRs and ... the list goes on). So Jira loads in an incognito window in a VM. But suffice to say that its local storage is even more _fucking obnoxious_.
> Tokens stored in those storages you mention can be read by any javascript code, even third party.
I don't doubt you. But I am not a javascript developer. I'd like it if you could link to some demonstrations of how that can be abused.