What's your computer system and Firefox version?

Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Firefox ESR; Extended Support Release {web link}

Beta, Developer, Nightly versions https://www.mozilla.org/en-US/firefox/channel/desktop/

Install Older Version Of Firefox {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

How to Start all Computers in Safe Mode; {web link} Free Online Encyclopedia

What's your computer system and Firefox version?

System Details (right from question details):

• Debian GNU/Linux 11, kernel 5.10 (amd64)
• Firefox 78.10.0esr

Um... Thanks for the described steps. I'm sure, it's not the case since I had an issue even on a newly-mainteined reinstalled system.

Are you currently using a version from the repositories of your Linux distribution? Try the Firefox version from the official Mozilla server: https://www.mozilla.org/en-US/firefox/all/

Are you currently using a version from the repositories of your Linux distribution?

This is not serious.

It is not an unfair question. Distro versions of Firefox can have missing crash reporting data and other changes whereas the Mozilla version is unaltered.

It is not an unfair question. Distro versions of Firefox can have missing crash reporting data and other changes whereas the Mozilla version is unaltered.

I ran the next session with the downloaded 78.11.0esr version with new profile, which still parses customized /etc/firefox-esr/firefox-esr.js preferences and got this log messages from the console:

• [Parent 15420, Main Thread] WARNING: FileDescriptorSet destroyed with unconsumed descriptors: file /builds/worker/checkouts/gecko/ipc/chromium/src/chrome/common/file_descriptor_set_posix.cc, line 19

• ###!!! [Parent][MessageChannel] Error: (msgtype=0x390060,name=PContent::Msg_SetPermissionsWithKey) Channel error: cannot send/recv

• ###!!! [Parent][MessageChannel] Error: (msgtype=0x39005C,name=PContent::Msg_GMPsChanged) Channel error: cannot send/recv

which do appear on every tab restart, when restart is required. Seems to be a new case for bug report.