hello ArgentLA, the file permissions.sqlite in your profile folder stores these kind of settings. if you suspect it has gone corrupted, you might try renaming it as well. also make sure that you've not set firefox to clear site preferences at shutdown in the options > privacy panel or that any of your extensions or external security/clean-up programs is interfering with the cookie handling in firefox.

another thing (though not related to your issue) - please turn plugin.expose_full_path to false in about:config since it might be a privacy issue when you browse websites

You can check the settings in extensions like Better Privacy to see if those are causing this issue.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

@philipp: As I stated in my original message, I do NOT have "site preferences" checked in the list of items cleared on shutdown. I doublechecked that before posting.

I also tried deleting and recreating the permissions.sqlite, but the problem recurred after doing that and I had to completely recreate the exceptions list again.

Thanks for the tip on the expose_full_path setting; I've fixed that.

@cor-el: I will try that, although the odd thing is that FF doesn't dump the exceptions list every time, just some of the time. After I posted this the other day, the list was retained most of the weekend without incident despite several restarts, but after restarting my browser a little while ago, the list is once again blank.

If you use cleanup software like CCleaner then check the settings for the Firefox application.

I do, but it's allowed to clean only the FF download history and cache (which theoretically are supposed to be cleared on browser exit, although I've noticed that since the FF 22/23 upgrades, downloads no longer clear unless I do it manually).

Also, I haven't been running the cleaner very often, so there's no correlation between that and the list disappearing. For example, FF dumped its cookie exceptions again earlier today, but I haven't run the cleaner since sometime last week.

Cookie exceptions (and all other exceptions) are only removed if you use "Clear Recent History" to clear the "Site Preferences" or otherwise remove the "Site Preferences".

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords (permissions.sqlite) and other settings from websites that Firefox stores like page zoom and download locations (content-prefs.sqlite).

I'm aware of that, which is why I don't have FF or the cleaner set to do that. I don't see any connection between that and the issue I'm experiencing, though, since neither the browser nor the cleaner is (or has ever been) set to clear site preferences.

@cor-el: Your comment got me thinking and I did some checking: While Clear Site Preferences was *not* checked in the "Clear history when Firefox closes" section, it had somehow gotten checked on the "Clear Recent History" tab. I don't know when that happened -- it was presumably accidental since I definitely didn't want that -- but that would explain why it kept happening and why it was intermittent.

I unchecked it, which I think probably resolved the problem, although now I feel like quite an idiot.

Thanks for your help!

You're welcome.