User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20170628030206 Steps to reproduce: I ran the latest Nightly 56.0a1 (2017-06-28) (64-bit) with many tabs I exited and opened Firefox 54.0 (the current stable version) Actual results: No tabs from the session were restored although I have the option "when Firefox starts" set to "Show your windows and tabs from last time" . There is just one blank tab. Expected results: The session should have been restored with all the tabs restored.

Some additional information: *) The session is not lost. I can't open it with Firefox 54.0, but when I exit it and re-open Nightly everything works fine, the tabs are restored. *) The session was restored without problems in Firefox 54.0 in the previous days with previous nightlies. I think the problem started with Nightly 2017-06-28, but I maybe wrong and it started a day or 2 earlier. *) Nightly runs in e10 (multi-process) mode, Firefox 54.0 runs in single process mode since e10s is disabled automatically by Firefox because I use an add-on (xmarks) that isn't compatible

A minor correction : when Firefox 54.0 opens without the sesstion restored , it opens with the Firefox start page, not with a blank page as I wrote. I can't change the bug title anymore, someone should update it to the correct description.

The bug still happens with the current Nightly 56.0a1 (2017-07-03) (64-bit), and the current stable Firefox 54.0.1 . I forgot to mention that it is always reproducible for me, tested on 2 different computers. Can anyone test and confirm it ?

Since the bug 934967 is landed, the session files produced by Nightly will be in .jsonlz4 extension, and thus can not be used in the stable Firefox version.

This is very annoying and as I understand will last almost 3 months until Firefox 56 is released at 2017-09-26 according to https://wiki.mozilla.org/RapidRelease/Calendar . Can't the session restore be made backward/forward compatible ? Nightly can for the meantime write an additional session store file in the old uncompressed format (in addition to the .jsonlz4 file), so that if I open the stable Firefox 54, it will be able to read my current Nightly session in the old format . When you switch back again to Nightly from Firefox release, it should check if there is an old format file (sessionstore.js, I believe), and if there is one, it should ignore the .jsonlz4 file (since the updated file is the .js file from the stable Firefox session), read the old format file and migrate it to a .jsonlz4 file, and then delete the sessionstore.js file (so that in subsequent launching of Nightly it doesn't try to migrate it again, since it will by then be older than the current session)

A small correction to comment #5 : Since according to my suggestion Nightly will have to write an additional backward compatible uncompressed file , its existence cannot be used to check whether the previous session was from the Firefox release (currently Firefox 54). Therefore the check by Nightly should be by comparing the date/time of the .jsonlz4 and .js files (or some session counter if there is one in use, to prevent problems due to clock changes etc.) If the .js file is newer, then it means the previous session was from a previous version of Firefox Release (54 currently), and it should be migated/compressed to the .jsonlz4 file. if the .js file is older, then it means the previous session was of Nightly , and it should use the .jsonlz4 file. When Nightly writes the additional .js file, it should write it first before the .jsonlz4 file, so that its date/time is older than the .jsonlz4 file.

Thanks, YF(YANG) . The bug state should be confirmed (NEW) based on comment 4 .

It sounds like this may be a known issue, and expected behavior. Sorry. And thank you for the thorough bug report. If you open a profile with Firefox 55 or 56 (or later, in the future) Then it is not compatible with older versions of Firefox, pre-55 versions. This is described in bug 977177, and in the release notes for 55: "Breaking profile changes - do not downgrade Firefox and use a profile that has been opened with Firefox 55+" So, not a problem with Nightly's session store, but rather that you opened a profile created in 56, with 54.

(In reply to Liz Henry (:lizzard) (needinfo? me) from comment #8) > It sounds like this may be a known issue, and expected behavior. Sorry. And > thank you for the thorough bug report. > > If you open a profile with Firefox 55 or 56 (or later, in the future) Then > it is not compatible with older versions of Firefox, pre-55 versions. This > is described in bug 977177, and in the release notes for 55: "Breaking > profile changes - do not downgrade Firefox and use a profile that has been > opened with Firefox 55+" So, not a problem with Nightly's session store, > but rather that you opened a profile created in 56, with 54. I would like this bug to be re-opened, since I think this is a wrong decision for the following reasons: *) I suggested a plan for a fix in comment #5 and #6 that seems to me very simple, does not involve a lot of work, and does not require changes in Firefox 54, only in the trunk (Nightly 56 ) : Nightly should save an additional session restore file in the old uncompressed format so that Firefox 54 and 55 can read it, and restore the session. *) Although bug 977177 had breaking profile changes, actually it seems they had no meaningful or critical effect at all . I constantly moved back and forth between Nightly 55/56 and Firefox releases 53/54 in the last couple of weeks without any problem. Maybe the bookmark favicons from Nightly didn't appear in release (if that was the bug about) but I didn't even notice that, because it was such a minor issue : favicons are not important or critical to web surfing. I guess they wrote the bug fix so that the Firefox release just used a default icon instead of the missing icon, or used the old one from the old schema of the db, and therefore there was no real problem with switching back and forth. The bookmarks themselves (not the favicons) were always updated when switching back and forth. *) Session restore, on the other hand (compared to favicons), is a major if not critical issue when moving back and forth between Firefox release and Firefox nightly. This is going to be a problem that will last about 3 months until Firefox 56 is released.

(In reply to nivtwig from comment #9) > I would like this bug to be re-opened, since I think this is a wrong > decision for the following reasons: > > *) I suggested a plan for a fix in comment #5 and #6 that seems to me very > simple, does not involve a lot of work, and does not require changes in > Firefox 54, only in the trunk (Nightly 56 ) : Nightly should save an > additional session restore file in the old uncompressed format so that > Firefox 54 and 55 can read it, and restore the session. I'm afraid that this is not really an option, even if this might seem easy; one of the main reasons for switching to a compressed format is because we want to reduce the disk I/O overhead and consumption. If we continue to write two files at the same time we'd re-introduce writing the uncompressed formats with all its downsides and imposes the burden of maintaining those two modes for the duration of the cycle for the benefit of a very small audience that actively switches between Nightly and more stable channels using the same profile. I'm on of the users in that audience, but I'm 1) too excited about the advantages of sessionstore becoming more stable and consume less disk space and I/O ops and 2) learned to use a different profile for web browsing and browser (or extension or web or other) development. We really try very hard to not introduce backward incompatible changes, and almost always succeed with that, but this time it really was an practically impossible option. Thanks for your thoughts and ideas, please keep them coming!

I just noticed this, running 56.0b1 rather than 55 stable version. (I'm unfortunately a "tab hoarder" who regularly opens too many tabs and then saves the recovery.js file to look at later - which of course I never do <eye emoji>[<smile>|<frown>]<question>). Could FF either implement a function in the preferences/file menu/etc to decode the jsonlz4 into the (previously at least) "normal" js, or a command-line utility to do so? I saw another thread that said the container format is Gecko-specific (https://www.reddit.com/r/firefox/comments/2ps6wg/jsonlz4_bookmark_backups/), so I guess I'll have the poke around to figure out how write an extension to execute it, and whether it will work with a 500-odd KB compressed file. Or just restart and use Save My Tabs once.

(In reply to jim.witte from comment #12) What I do in order to overcome this problem ( which will be here until Firefox 56 is the release version), is to use "bookmark all tabs" in Nightly to save the tabs to a bookmarks folder. Close Nightly and then start the release version (54 or 55), and open all the tabs in the bookmarks folder created using "Open all in tabs". It will not save form data in the tabs etc. , but will restore all tabs.

> … decode the jsonlz4 … Cross reference: bug 1209390 - Use standard lz4 file format instead of the non-standard jsonlz4/mozlz4 <https://bugzilla.mozilla.org/show_bug.cgi?id=1209390> (2015-09-28) Also, from <https://unix.stackexchange.com/questions/326897/how-to-decompress-jsonlz4-files-firefox-bookmark-backups-using-the-command-lin#comment711099_338880> (2017-10-15): > The andikleen solution is also good for .json.mozlz4 …