[Bug] When re-entering Fenix, occasionally toolbar UI is missing

[nyanpasu64]

Steps to reproduce

• Install Firefox Preview (I built from source).
• Switch to another app which uses lots of RAM, so Android unloads Firefox.
• Reopen Firefox Preview.

Expected behavior

Upon trying to replicate this bug, I end up on the tab list, with all tabs intact, and the UI functional. I feel this provides a "clean slate" so I can enter a new search term instead of reading old tabs.

Alternatively (to match Firefox Android), the page and toolbar would be present, and I can enter a new URL and switch tabs.

Actual behavior

One time, I ended up on the webpage I was reading (either back one history entry, or on the page I was reading), but with the toolbar missing, replaced by a black/gray void at the bottom of the page. Page scrolling did not work at first, but later started working. I had to restart Firefox Preview by swiping from Recent Apps and relaunching (which brought me to the tab list) to make the toolbar come back.

I took some Android Studio layout captures of Fenix in the no-toolbar state, as well as the normal state after restarting.

Comparing the layout captures, in the bugged layout, id/toolbar is missing and id/nestedScrollQuickAction has no children.

Device information

• Android device: Moto G5 Plus, stock 7.0 with Magisk
• Fenix version: master bfd4849 (with gradle.properties org.gradle.jvmargs edited to reduce memory consumption)

Possibly related to #4461 '[Bug] When re-entering Fenix, open tabs all change to "about:blank"'? This time, my tabs were still there and not replaced with about:blank. In the past, I experienced this issue.

┆Issue is synchronized with this Jira Task

[rituraj22]

The same happened on Nightly 190802 18:05 (Build #12141932) build in my Android 9.0 phone

[jacktose]

Confirmed on Nightly 190802 18:05 (Build #12141931), Android 8.1.0, Moto G5+.
It's been happening occasionally for a few days, possibly since the 190802 build.

I'm also experiencing #4461, but that's been going on a long time and this is new.

[ekager]

IIUC this should be fixed by #4412
Is that right @csadilek ?

[nyanpasu64]

#4412 was closed 5 days ago. I think my master checkout was from 2 days ago.

[colintheshots]

I can't find steps to reproduce, but I can determine why the toolbar and quick action sheet both might go uninflated. That should be enough to produce a fix, but I'm not certain how to test the fix yet.

[csadilek]

IIUC this should be fixed by #4412
Is that right @csadilek ?

@ekager This looks like it could be related (caused by the same problem) I described in #4427. It's possible for the BrowserFragment to be created before the sessions have been restored. Without a sessionId we're not creating the UI properly.

[abodea]

Verified as fixed using latest debug build(from the master) 1.0.1933(build #1) 8/14 with Samsung Galaxy s10+(Android 9), Huawei P9 Lite(Android 6), Samsung Galaxy S7(Android 7).
Please note that I tried to reproduce this issue following the steps from the description but the issue cannot be reproduced.

Also, I tried the following:

1. Start the download of few big apps from Play Store.
2. Open more apps that are using a lot of RAM.
3. Launch Fenix.
4. Open few tabs.
5. Switch between apps.
6. Re-open Fenix.

But everything worked as expected. I will close this issue and re-open it in case we will be able to reproduce/see this bug in the future.

[nyanpasu64]

Happened twice to me after this issue was supposedly fixed. I think it's less frequent but still happens. First time an older build, with no tabs open. Second time on a build from 2019-08-15, with tabs open.

Interestingly, both times, I got a white screen with "pull to refresh" enabled. Otherwise, "pull to refresh" is not enabled.

[jacktose]

I've also had this a few times since the fix, on 1.3.1.

[nyanpasu64]

I think this is the same issue as #12490, and I just hit it again on Nightly 200830, but was unable to take a layout capture.