After moving from a very old Ubuntu (with Firefox 3.0 + Sync as add-on) to Linux Mint 13 MATE (with Firefox 15.0 + Sync as core functionality) I had a very strange and unpleasant surprise -- my Firefox Sync Key is not valid anymore. I am sure that the key I'm typing is correct (I have two equal copies of it). My Firefox Sync account is also active (it accepts my e-mail address and password).
After a quick research I have found that people have similar problems but no one has found any satisfying solution yet. There is also a difference in the key format (old: xxxxx-xxxxx-xxxxx-xxxxx, new: x-xxxxx-xxxxx-xxxxx-xxxxx-xxxxx) and in its name (old: Sync Key, new: Recovery Key). Everything indicates that Mozilla has really changed the key format for the Sync service. But what happens with users switching to newer Firefox while still holding a key in the older format? Is there any way to get my data back from the Sync server now? Maybe there is an algorithm to calculate a new key while having the old one? I should be grateful for any help coming from you.