Hi, @Zosha:
In addition to @torchwood's excellent advice...
Many times, problems with TB (or Firefox) originate in the user's profile, rather than in the program itself.
Before reinstalling TB, you might try the
TB - standard diagnostic
The article is
a bit quite dated, but the general procedure (e.g. beginning with starting TB with add-ons disabled, aka "Mozilla Safe Mode", and then backing up one's profile BEFORE proceeding to reinstalling the program) is a good idea.
Your data (address book, mail messages, account settings, etc.) are stored in the user profile, not in the program itself.
So, it **ought** to be safe to reinstall TB.
But, it might be
safer to backup the profile (using
Mozbackup or
TEBE or another method)
BEFORE reinstalling the program.
(Neither of those backup utilities is still being actively developed, but AFAIK they both still work.)
Also, the
article I linked above explains how to *cleanly* reinstall the program, if you wish to do so.
AND, you might try compacting folders and deleting the msf folders, as explained
HERE.
(But again, I would backup the profile first.)
Additional info here:
Thunderbird support
Please let us know how things go.
Thanks,
MM