###!!! [Child][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost

Hello! I am running firefox-esr version 68.5.0esr-1+b1 (from Debian testing) with a bunch of extensions (ublock origin, multi containers, suspend tab, open in browser, all in one sidebar, etc). Yesterday, I was suddenly unable to start firefox. I can see the profile manager and start another older profile, but not the one I really need to open. When I start from a terminal, I see this error message most of the time: ###!!! [Child][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost I have created a new profile and started it with success; after copying all files from the faulty profile, the new one does not start. I have tried to run with safe mode: still does not start. I have found https://unix.stackexchange.com/questions/426502/firefox-keeps-crashing-upon-launch/466522 which doesn't help. https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile shows me how to copy bookmarks and cookies over. (I am not using any synchronization service.) I would very much like not losing my session (open tabs), but I don't know which file or database is holding it. I would prefer not to have to spend a lot of time reinstalling and reconfiguring all extensions, but maybe it will be necessary. Thanks for any help troubleshooting this.