Does Firefox's private browsing mode store anything (like cache files) to the hard drive?
When a user browses the web on Firefox's private browsing mode, is ANYTHING about the user's activity stored onto the hard drive (like browsing history, and more importantly cache files), even for an instant?
I know that the private browsing page says that it does not "save" this information, but that is kind of ambiguous as to how this data is actually handled. When you visit a page in private browsing mode, does Firefox store information and cache ONLY in the computer's RAM and never touches the hard drive, OR does it save data and/or cache onto the hard drive for a short time while while the private browsing window is active, and deletes it after you close the window? This distinction is extremely important because data saved to the hard drive, even for an instant, can be recovered by a file recovery program, or worse, by malware that collects data.
Has how Firefox handles what I talked about ever changed from version to version? What about on Android and iOS? Does private browsing behave differently on mobile?
I would extremely appreciate it if someone with a lot of experience with how Firefox works, or better yet, someone who works for Mozilla, can answer this question. Thank you.
I ask this question because a previous question asked almost two years ago claimed that Firefox's private browsing mode does indeed save data to the hard drive:
https://support.mozilla.org/en-US/questions/1107450
The question and (as a result) its answers were kind of ambiguous as to what Firefox's actual behavior was, so I am asking this question in hopes of obtaining a clearer answer about how Firefox handles data storage. Firefox is often praised as a privacy oriented browser, and as such, I feel that informing users of this information is vital.
Modified by x100
All Replies (8)
When you are in Private Browsing, everything goes to a temporary folder. When Firefox is closed, that folder is removed.
FredMcD said
When you are in Private Browsing, everything goes to a temporary folder. When Firefox is closed, that folder is removed.
So private browsing DOES save data to disk? Does this include cache files?
Is there an official documentation stating this? How do you know? I am confused because I have heard other sources say that Private browsing keeps everything in RAM, like this question: https://support.mozilla.org/en-US/questions/1106003
Modified by x100
Everything.
https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history Private Browsing - Use Firefox without saving history
FredMcD said
Everything. https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history Private Browsing - Use Firefox without saving history
Everything is still saved to the hard drive, you mean? Because there seems to be no mention of that in the link you included.
Modified by x100
x100 said
Everything is still saved to the hard drive, you mean?
Temporarily. When you close the browser, the data is removed.
In principle, private session data is not written to disk. When I create a new profile and set it to run in automatic private browsing mode, Firefox does a lot of automatic background retrievals that show up on the about:cache page, Disk cache category. A strangely large number of Amazon requests, for example. However, my own browsing does not show up there and I do not see history written to disk when I look at files in the profile folder.
All data is kept in memory during the PB mode session. When you only open a PB mode window then regular cookies and other data is swapped to the hard drive (profile folder) and in memory storage is set up including a separate cookie jar. There is no persistent storage available and all in memory data is purged once all PB mode windows (tabs) are closed or when you close Firefox.
cor-el said
All data is kept in memory during the PB mode session. When you only open a PB mode window then regular cookies and other data is swapped to the hard drive (profile folder) and in memory storage is set up including a separate cookie jar. There is no persistent storage available and all in memory data is purged once all PB mode windows (tabs) are closed or when you close Firefox.
So PB mode stores nothing to disk then? Not even temporarily?
What if you open a PB mode window and a regular mode window? The only information reaching the hard drive is about the regular mode windows, right?
What about on mobile like Android and iOS? Is the behavior the same?