HI Amir, I don't know why Firefox Sync is having that effect on your Linux installation. I don't think cookies are shared through Sync, so it's difficult to imagine a direct connection.

It is possible that some sites will invalidate the session related to your cookie if some of your connection parameters have changed, which they may consider suspicious. Certainly this can happen with sites that don't like a variance in the IP address, and they may not like a change in the user agent string, either. But that's just a guess.

Are you possibly sharing the same profile folder between Windows an Linux as that might be causing issues ?

@jscher2000 Hi, I do not think cookies will sync too. I just said maybe the cookies deleted in Debian. Few minutes ago I used Firefox in Windows and now come back to Debian to reply this topic and I have logged out from this website. But not from other websites like Google and Atlassian and more... which log outed the last time I used Windows and then come back.

@cor-el No, I did not shared profile.

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Cookies
• do not clear the Site Preferences

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an allow exception you may want to keep

Between the times you used this site in Linux, did you use your Firefox Account to sign in to this site from Windows? If not, I don't have any theories about why your session on Linux ended.

Between the times you used this site in Linux, did you use your Firefox Account to sign in to this site from Windows? If not, I don't have any theories about why your session on Linux ended.

No I have not even visit this website.

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Cookies
• do not clear the Site Preferences

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an allow exception you may want to keep

I use Firefox in Debian everyday, But when use it in Windows have problem in Debian. Even if this setting turned on in Windows (I know its not) It should clear cache and history in Windows, And should not affect about Cookies and caches in Debian. Right?

You shouldn't have a problem with cookies between Debian and Windows unless you use the same profile folder in both cases like I wrote above, but you wrote that you didn't. Sync doesn't affect cookies, but you can sync cookies settings like for clearing cookies

You can check the compatibility.ini file in the profile folder to be sure as this files stores a link to the Firefox installation folder that last used this profile.

You can also try to exclude the preferences from Sync.