Uninstall the beta version, then install 78, but don't run it at the end of the installation. Open a Run window (Windowskey+R) and type

thunderbird.exe -p --allow-downgrade

to open Profile Manager, then select the profile that was used with the beta. That should allow 78 to open the profile used previously in 88.

Thank you very much. 78 works properly now and i have recovered all my emails !

But not my adress books (collected adresses...), do you have any idea how could i get them from my last profile backup now?

In your profile folder, do you have abook.sqlite, abook.mab.bak, history.sqlite and history.mab.bak?

Yes i have... all files were copyed from the beta version

The sqlite files should have transferred, but if not, rename them by adding .bak, then rename abook.mab.bak to abook.mab, and history.mab.bak to history.mab, with TB closed. Restart TB and see if the contacts appear in Personal Address Book and Collected Addresses.

Still no contacts I renamed abook.mab.bak to abook.mab, and history.mab.bak to history.mab,

Hi In fact TB collect no adresses since i have installed it .... Do you have an idea ? Thank you for your precious help.

If you followed the earlier instructions, I don't know why the contacts didn't appear. You could try this: with TB 78, Help/Troubleshooting, about:profiles, create a new profile but don't add any accounts. Open the new profile folder from about:profiles, close TB, delete abook.sqlite and history.sqlite, copy in abook.mab and history.mab, restart TB in the new profile and see if Personal Address Book and Collected Addresses have the contacts. If they do, copy abook.sqlite and history.sqlite into the other 78 profile folder, then restart TB in the other profile, the one with all the account data.