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Determine version of Firefox last used by a profile backup
I keep an archive of profile backups on an external hard drive. The backups are compressed, and I usually include the version of Firefox last used by the (principle) profile in the compressed archive filename (e.g., userinfo-firefox-56.0_date). I also make a semi-regular sync backup of the currently used profile. So far, so good.
My currently synced backup, which has not been compressed and archived, is about a month old. (I did say semi-regular.) I would like to compress and archive it before syncing, but I am no longer sure of the exact version of Firefox it used. I usually run updates when released, and can suppose Firefox 65.x, but what if I would like to be more exact? After running a search of files containing "version" in the main profile, I came across a file named compatibility.ini, which resides in the root directory. The contents are as follows:
[Compatibility] LastVersion=65.0.1_20190211233335/20190211233335 LastOSABI=WINNT_x86_64-msvc LastPlatformDir=C:\Program Files\Mozilla Firefox LastAppDir=C:\Program Files\Mozilla Firefox\browser
Is this a reliable way to detect the last version of Firefox used by the profile?
Like you already discovered: compatibility.ini stores this information (version and build info). This data its used to reinitialize a profile if Firefox detects that the version that last used the profile is different than the version that started this profile. See also the application.ini file in the Firefox program folder.Read this answer in context 👍 1
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A good idea, but you don't really need the old, old files anymore.
Note: Some versions of Quantum change how the data files are set up, so they are not backward compatible.
Edited for clarity: The data in the old profiles and how it's organized is the interesting thing. For instance, Scrapbook data and used tabs that no longer exist in my current profile. If necessary, I could temporarily install a compatible version of Firefox to access the data. So throwing away archived profiles is not the issue.
Where could I reliably find the version of Firefox last used by a profile?
Modified by michapma
Like you already discovered: compatibility.ini stores this information (version and build info). This data its used to reinitialize a profile if Firefox detects that the version that last used the profile is different than the version that started this profile. See also the application.ini file in the Firefox program folder.