[acqq]

If I understood the intention of the programmers, they simply want to store "everything that can imitate to the server the continuation of the current session" even after the new start of the Firefox (like the restart never happened). The images were sent by Google, but probably remain in the DOM tree which is then written as the "session data" or something like that.

Like you, I also observed that exactly the people who depend on the tabs to "remain" after the restart are those who are hit by the bugs in the "restoration" and as I've said, I believe the users would more prefer to have "stable" tabs and URLs than the "fully restored sessions in the tabs" when all the tabs fully randomly (for them) disappear. Maybe saving just the tabs and URLs separately from "everything session" would be a good step to the robustness (since it would be much less data and much less chance to get corrupted) and then maybe, pretty please, an option "don't save session data" can be in the about:config too)?

Once there's decision to store just the URLs of the tabs as the separate file, the file can even be organized in a way that just the URL that is changed gets rewritten, therefore making the "complete corruption" of the file impossible and also removing the necessity for Firefox to keep N older versions of the big files (which then eventually still don't help the user like you).

[alphapapa]

> Maybe saving just the tabs and URLs separately from "everything session" would be a good step to the robustness (since it would be much less data and much less chance to get corrupted)

Yes, that would be very, very useful. I can get by if the tab's scroll position and favicon and DOM-embedded images--and even formdata--are lost. But if the tab itself is lost, and it was a page I needed to do something with, I may never even realize it is gone...