I do not think anything much has changed with the Firefox system restore files and how they are handled so it may be possible to keep these and use them after an upgrade in a new version of Firefox.

It is very important that you backup the Firefox profile see

• Back up and restore information in Firefox profiles

If you do that you will be able to use the open tabs again.
(May need to reinstall Firefox 3.6 again possibly as an additional browser)
You must

• Put that profiles somewhere safe. NOT in the Firefox profile or program path. Your Window's Desktop is ok as a safe place.
• When needed. Only work with copies of those files. Keep the original files and folders safe.

Upgrade to the latest Firefox. Because you are going up so far from 3.6 to 27 do this by installing the new Firefox 27. Do not try using each upgrade step from 3.6 to 27.

Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not run Firefox's uninstaller or use a third party remover as part of this process, because that could permanently delete your Firefox data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords.
These cannot be recovered unless they have been backed up.
(That is why I asked that the profile was backed up FIRST)

You may be surprised and find Firefox still has the old tabs once it is reinstalled.

Post back with how you get on. We should be able to get access to the old tabs again.

In future I suggest you do not try to rely on keeping 300 tabs open all the time without bookmarking them. You will at some stage probably lose some or all of these tabs, or their related states and history.

Please in future

• Backup your profile on a regular basis.
  • Once a week means you may only lose one week's open tabs.
• Bookmark important open tabs.
  • Bookmarks keep well.
  • Open tabs do not keep well & may be lost.
• If possible reduce the number of open tabs you use.

already installed but all login site became logout. and when do right-click on page too many list.... and when i choose open in new tab or windown and other nothing happened...... loading on page became more long (already stop other tabs) and when i block some text/link and drag it to tab or navigation input text or search input text nothing happenend too.....

and when i close, no choice for save and quit......

edit:

Solved:

1. Save and quit already solved using addons.

2. right click and drag problem already solved, I close firefox and restart it.

not solved:

1. All login site still in logout condition (can't stay login like before).

edit:

not solved:

2. on option, image block list is missing.

already installed but all login site became logout. and when do right-click on page too many list.... and when i choose open in new tab or windown and other nothing happened...... loading on page became more long (already stop other tabs) and when i block some text/link and drag it to tab or navigation input text or search input text nothing happenend too.....

and when i close, no choice for save and quit......

edit:

Solved:

1. Save and quit already solved using addons.

2. right click and drag problem already solved, I close firefox and restart it.

not solved:

1. All login site still in logout condition (can't stay login like before).

edit:

not solved:

2. on option, image block list is missing.

Modified February 17, 2014 7:06:03 PM PST by Allen Walker

no one answering?

Details like websites remembering you (log you in automatically) are stored in a cookie.

• Create a cookie 'allow' exception to keep such cookies, especially in case of secure websites and when cookies expire when Firefox is closed.
• Tools > Options > Privacy > Cookies: Exceptions

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

It is possible that the cookies.sqlite file that stores the cookies is corrupted if clearing cookies doesn't work.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookies files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies

You can inspect and manage the permissions for all domains on the about:permissions page or for the domain in the currently selected tab via these steps:

• Click the "Site Identity Button" (globe/padlock) on the location bar
• Click "More Information" to open "Tools > Page Info" with the Security tab selected
• Go to the Permissions tab (Tools > Page Info > Permissions) to check the permissions for the domain in the currently selected tab

• https://support.mozilla.org/kb/how-do-i-manage-website-permissions

Delete the permissions.sqlite file to reset all permissions.