Currently the Firefox profile migrator ignores any extensions or themes that may be installed in the profile to be migrated. It seems that once bug 329744 is fixed, simply copying the files from the old profile's extensions directory will cause them to be loaded and installed. Any extension that doesn't list Seamonkey in it's compatibility list will be disabled, which means that there isn't much risk involved. Also, the extension manager will automatically check for compatibility updates to the extensions. Of course, migrating extensions from old seamonkey profiles is probably not feasible, though we could note the id of the extension and automatically download the xpi from AMO to install.

Themes should not be migrated. They aren't even compatible between different versions of Firefox.

(In reply to comment #1) > Themes should not be migrated. They aren't even compatible between different > versions of Firefox. > Isn't this sometimes also true of extensions? I'd imagine this will become "WONTFIX".

(In reply to comment #2) > Isn't this sometimes also true of extensions? I'd imagine this will become > "WONTFIX". > I imagine the same, alas.