My windows 10 machine died on me recently, but I was able to recover all my Thunderbird Email files from the old hard drive. However, the Thunderbird settings I was using under Windows 10 did not transfer over to the new machine and there is one particular issue which is driving me crazy and I don't know how to fix:

Basically, on my previous machine I frequently filtered my emails using the threaded option based on the Subject field. However, under Windows 10 the filter I was using would ignore the "Re:" in the subject line of such threads and so every message in the thread was displayed as if the various instances of "Re:" simply weren't there. However, on my new machine Thunderbird threads messages as if each instance of "Re:" represents a new thread! How do I fix this?