Fennec migration: Clarify if Gecko profile will be re-used

[pocmo]

It is unclear whether the Gecko profile will be re-used after paving over Fennec. This may affect whether we continue to use data like:

• Cookies
• Website Cache
• about:config flags (We were consider nuking them since there's an endless combination of configurations that we may not be able to support correctly).

┆Issue is synchronized with this Jira Task

[st3fan]

Personally I think it is more important to get people in a known predictable state. Which may probably not happen when we carry over an existing profile.

If we go this way: what data do we need to import from the old profile?

[snorp]

My gut feeling on this is that reusing the profile should be ok, with the exception of prefs. We should remove the prefs.js file in the profile directory.

[ebalazs-sv]

Hi!
I verified this on Fenix Nightly 191127 GV 71, with Pixel 2 (Android 9), Samsung Galaxy S8 (Android 9), Huawei Honor 8 (Android 7.0), Nexus 6P (Android 8.1.0), Xiaomi Mi Pad 2 (Android 5.1), ARM, ARM64 and x86 devices.

For Cookies:

• The items from the sportsdirect.com cart are available after the migration.
• The user is logged in on facebook.com after the migration.

For Website Cache:

In about:cache different values are available after the migration, for example:
disk values

• on Fennec 832 -> on Fenix 654
• on Fennec 530 -> on Fenix 409

memory values

• on Fennec 3 -> on Fenix 0
• on Fennec 5 -> on Fenix 0

@pocmo Is this behavior for Website Cache expected? Do you have other suggestion for testing the Cookies, Website Cache migration? The about:config is not available on these builds. Thanks!

[pocmo]

I assume this is fine. @snorp any concerns?

[ebalazs-sv]

Verified as fixed on today's Release, Beta, Nightly migration build 12/16 with Huawei Honor 8 (Android 7.0) the scenarios from the previous comment.
I will move this to Done.