After having to wipe and reinstall back up, using Yosemite, I lost several email folders and add-ons, new add-ons have download "save to" window not install now

Question

I installed Yosemite but it didn't go right, had to get Apple techs to help wipe and reinstall. Migrated apps and files from time machine backup. Thunderbird did work before things got bad enough I had to do something about Yosemite install problem.
Thunderbird lost several folders I sort mail into, and all but one extension. I tried reloading Thunderbird app support from older back up, nothing changed. I re-downloaded and installed Thunderbird. No change.
New extensions show download window with "save as" or "open with options", not the normal install button.

Answer 1

There may be one or more large folders in your /Volumes folder that shouldn't be there and are using up your disk space.
/Volumes is an 'invisible" folder at the root level of your internal drive which is supposed to contain only the "mount points" for your attached disk volumes, but sometimes an actual folder can mistakenly get created there, often as a result of a failed copy operation such as you experienced with SuperDuper. Such a "ghost" folder will have a name similar to a real external drive, and can contain data that was meant for the real external drive but never got there. When the real external volume then re-mounts, it can no longer use its own name for the mount point in /Volumes because that name is already "taken", and so an extra number gets appended to the mount point. This may have happened twice in your situation, since the actual drive is now mounting as "Untitled 2".
/Volumes is a hidden folder, but it's easy to peek into it. First you should *eject and then physically disconnect all external drives*. Then:
Finder>Go menu> Go to Folder
enter /Volumes and click Go
You should see an alias to the startup volume. Don't touch this, or any other aliases. Do you also see a large folder named "Untitled, and perhaps another folder named "Untitled 1," which are not aliases? If so, delete them, and restart.