User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.101 Safari/537.36

Steps to reproduce:

Browsing multiple pages with more than 9 Firefox windows opened, 5 or 6 of them with only a tab and other with 3 to 7 tabs, my typicall way or working without issues till now.

Actual results:

Firefox does not respond unexpectly to anything, needing to kill that Firefox window (and therefore, all Firefox opened windows)

Expected results:

To browse normally.

The Bugbug bot thinks this bug should belong to the 'Firefox::Session Restore' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Hey rafael,
I tried reproducing this issue on the latest versions of Firefox Nightly 91.0a1 (2021-06-15), beta 90.0b8 or release 89.0 but no hangs were encountered for me.
Can you test the issue while in Safe Mode? You can find helpful info here : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode .
Also a fresh new profile could help. You can find more about creating a new profile here : https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems#w_6-create-a-new-firefox-profile .
If possible, you can test this issue on the nightly build as well. Download the build from : https://www.mozilla.org/en-US/firefox/nightly/all/ .

I'll try in safe mode. Anyway, I'm sure I'm not the only one affected by this issue. In fact, I found another one in Reddit https://www.reddit.com/r/openSUSE/comments/o1qsr6/firefox_89_hangs_randomly/

I must add that in my case, the two PCs are using a corporative proxy (without issues in any previous Firefox version).

Most likely a duplicate of bug 1714779. When you hit the issue again could you try to follow the steps in bug 1714779 comment 11 and post the resulting info on that bug?