User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:83.0) Gecko/20100101 Firefox/83.0
Build ID: 20201004212809

Steps to reproduce

1. In a new profile, install Temporary Containers and Ghostery. Make sure their toolbar icons are visible.
   (Because they have obvious tells when bug occurs)
2. Install another 20 to 30 random extensions. You can choose from this Recommended Extensions list.
   (Because they are manually reviewed and should have higher code qualities.)
3. Open Browser Console.
4. Restart browser either by Ctrl-Alt-R on Browser Console, or by the button in about:restartrequired.

Actual result

(Please refer to the attached video.)
Some extensions may not work after restarting. In the case for
Temporary Containers: its toolbar icon shows there is an error. Clicking it will open a tab showing more information.
Ghostery: clicking its toolbar icon does not bring up its panel.

Expected result

All extensions should work after a restart, no matter how I restart the browser.

Notes

A. The bug does not occur when

1. restarting from about:restartrequired without Browser Console;
2. restarting from the bi-daily Nightly updates. (It might, but I haven't seen it for about a week.)
3. closing the browser completely and re-open it.

B. The combination for installed extensions does not matter. The more extensions are installed, the easier the bug can be reproduced. (I can even reproduce it with just Temporary Containers and uBlock Origin; but it is very rare.)

C. Temporary Containers and Ghostery are not the only affected extensions. Some other extensions include but not limted to

1. uBlock Origin: toolbar panel does not expand correctly. Some settings are lost.
2. uMatrix: I cannot connect to the internet at all only from the browser.
3. ClearURLs: toolbar panel does not initialise correctly.

Workarounds

1. Disable and re-enable affected extensions, or
2. Close the browser completely and re-open it.

From Mozregression:
Last good Nightly: 2020-08-20
First bad Nightly: 2020-08-21
pushlog: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=e375b85cfba38ff5f49493d1d48b7561f7f2f8d7&tochange=432e42cbbc4139efd2319952ec33efe8ff9add3c

Bisecting autoland builds:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=1c19feaebe2816c4297f3e4b1b44b37ef922a324&tochange=2839eaa25b4e0d4185b938df1ecff76ee85d3f1b

This is regressed by bug 1657310.
I understand WebExtenions and devtool are kind of unrelated, so I leave the regressionwindow-wanted keyword in the bug report.

Alternative STR:
0. Install many extensions.

1. Restart browser with about:restartrequired. No need to open Browser Console at this point.
2. When browser is restarted, quickly open Browser Console before affected extensions finish initialising.

Confirmed with 83.0a1 (2020-10-05) on Windows 10.
Updating some fields, @Fanolian thanks for the complete report!

Nicolas, can you please take a look at this?

I can't reproduce it.
Cristian, how many extensions did you had to install to trigger the issue.
Is this still here in 85?

I can still consistently reproduce the bug in my main profile in Dec 7th build, but it becomes rare for my test profile for this bug (maybe 1 in 30 tries).
The improvement came around mid November (Nov 11~14). It is entirely subjective so I cannot give a precise commit range for the improvement.

I do not want to share my main profile. Here's the test profile I use for this bug:
https://wetransfer.com/downloads/1e253f4603ed612c0d87db610804af3320201207160554/75c41c
(I think BMO does not support large file upload?)
The link expires in 1 week.

Name: 9xozp75v.Extension_initialisation.7z
Size: 86693566 bytes (82 MiB)
CRC32: 51C6871D
CRC64: 664DC14D9E8542D2
SHA256: 461E35F70D04AB21B6CEE320BCC09E91B2226A8DFBD3BEB51E8F6EC96C1667FA
SHA1: 523027B88215D59B83D1AA9DEDA8A601823A1F5D
BLAKE2sp: 6EBC28BF1C499FCE30C7FD0CEF33D9CE71E2DAD7F03D436A42947B4592899B23

https://www.virustotal.com/gui/file/461e35f70d04ab21b6cee320bcc09e91b2226a8dfbd3beb51e8f6ec96c1667fa/detection

There should be minimum personal info in the profile (hardware info, system language,...). No login sessions are ever entered.

P.S. Please open google.com as the active tab when testing. The tab would not load when uMatrix fails to initialise.

Recieved bug from crostian.fogel and I managed to confirm the issue using the latest Nightly 85.0a1 (2020-12-08) on Windows 10 x64 with 19 add-ons installed. I used the exact same steps from comment 0 and the video and got the same result as in comment 0. But after a few seconds the Ghostery and uBlock Origin add-ons seem to work as expected. On the other hand the Temporary Containers still display the error throughout the whole session.

However I did notice that the cookies popup window for Google doesn't load when uMatrix is enabled. So I am thinking that this is another issue.

This might have been fixed by either bug 1687657 or bug 1728290.