I have lots of backup and restored my .cache/thunderbird and .thunderbird from 3 weeks ago and force installed 68.12.0
If you are on the old Thunderbird - save those files before exiting Thunderbird and starting 78.4 or you cannot install the older version.
the new folders take more space on the desktop and you cannot get multiple to cc or bcc - you have to drop them in the single slot.
I “zypper addlock MozillaThunderbird” to prevent 78.4 from re-installing.
Not even if you do a one-off start from the command line of “thunderbird --allow-downgrade” ?
the new folders take more space on the desktop
Didn’t make the comparison myself, my TB 78.4.0 is currently occupying 57.5 MiB (60,274,497) in ~/.thunderbird, excluding the mail directory. I’ve no idea how much space was occupied prior to the 78.* version…
and you cannot get multiple to cc or bcc - you have to drop them in the single slot.
Yes, I’m not too pleased with that change to the compose window myself 
… There’s some discussion over at the mozillaZine Forums as well, just two threads for example:
Disgusting new Thunderbird - mozillaZine Forums (Note the second post by “@tanstaafl”)
spoiled functionality in the version 78.2.2 - mozillaZine Forums
78.4 changes the config files - new are not compatible with 68.12 - you have to start over with a new config file if you want to go back to 68.12.
Hmm… OK. “Something” must have been change recently then, as not long ago I used the --allow-downgrade option to go from TB 78.2.2-3.3 to TB 68.12.0-1 due to this 1176384 – mozilla/thunderbird78: Thunderbird Starts up Blank after Upgrade to 78.2.2 bug.
At that time I had TB 78.2.2-3.3, temporarily replacing that with TB 68.12.0-1.1 and then launching TB from the command line with --allow-downgrade launched without any problem using the 78.2.2-3.3 profile. In that instance I didn’t extensively test it, but all looked OK, accounts and mail present, able to send and receive mail…