Good questions, Sam.
The short answer to all of your questions is: Usually you can just export, but because Xmarks has been involved previously, it would be better to do the housecleaning.
Here's the long answer
Deleting all of the built-in ("local") bookmarks in both browsers is not necessary because BookMacster will do that when you click
Bookmarkshelf >
Export.
If iCloud is currently behaving itself (updating among your devices), you don't need to switch off iCloud/Safari syncing. However, if you ever used
Xmarks for Safari, there is a chance that there may be at least a few orphaned records in iCloud or Safari, which might result in more horrendous trouble after you export many changes. Therefore, if you've ever used
Xmarks for Safari, it would be a good idea to
rebuild your iCloud bookmarks first (which changes my answer in the previous section, because it requires deleting all of your Safari bookmarks).
Regarding Xmarks for Firefox, the answer is that doesn't matter if you turn it off and back on later, or just leave it on; it will probably do the same thing either way, as long as Firefox is running during the export. BookMacster may advise you to quit Firefox to save time, but don't. However, since I don't know how Xmarks for Firefox works, again, it would be better to delete all of your bookmarks from Xmarks (and, consequently, Firefox) before proceeding.
Although we tested BookMacster with Xmarks for Firefox a long time ago, we've done more recent testing with Firefox Sync, and I would recommend using the built-in
Firefox Sync instead of Xmarks. Warning: Complexity ahead
Neither Xmarks for Firefox nor Firefox Sync will see the changes occur if Firefox is not running. Although long ago we found that this Xmarks had the capability to catch up later, Firefox Sync does not, which is why BookMacster launches Firefox prior to an export, but only if Firefox Sync is in use. However, if Firefox is not running, even if Xmarks catches up later, changes will not be synced to your other devices until the next time Firefox is launched. Hmmm. We should probably have a setting in BookMacster to
always launch Firefox before exporting to it, for Xmarks users. I've just added that to our to-do list.
Just to be clear, when you say
set the two browsers to sync with BookMaster, that is done in BookMacster, by hitting the
Syncing button in the toolbar so it turns green.
Finally, regarding not messing up the work you just did, remember that if you have Mac OS 10.7 or later, even if something dumps a load a crap on one of your browsers, and BookMacster dutifully imports the crap, you can always restore to a previous bookmarks by using the
Auto Save and Versions feature of Mac OS X, and then exporting from BookMacster back out to the browsers. If you're on an earlier Mac OS X, you can still do it, with a Time Machine or other backup of that .bkmslf file.