STR: * disable the bookmarks engine, sync. * enable the bookmarks engine, start syncing. * quit Firefox before sync completes. * restart Firefox, note that about:preferences#sync still says bookmarks is enabled. * sync. * Note that bookmarks were not synced and the engine became disabled. Probably not a huge deal as it should be somewhat rare, but possibly worth investigating in case we can identify other related issues that are more likely to be hit.

Perhaps related to Bug 608231.

I'm fairly confident I've seen this happen in practice (when tracking down the source of slowness for bug 1296560) and there seems to be a case (or every case?) where we don't totally recover -- e.g. bookmarks never syncs again, and nothing allows it to get readded to the set of enabled engines. I didn't dig into it at the time, but I still have that profile and made a mental note to look into it more later (Of course, it's also possible this is a separate but unrelated issue).

(In reply to Thom Chiovoloni [:tcsc] from comment #2) > I'm fairly confident I've seen this happen in practice (when tracking down > the source of slowness for bug 1296560) and there seems to be a case (or > every case?) where we don't totally recover -- e.g. bookmarks never syncs > again, and nothing allows it to get readded to the set of enabled engines. It would be great if you can try and reproduce this - that would be a much larger problem than I see here (where I believe bookmarks is re-enabled as soon as the next sync completes)