*** BACK UP BOOKMARKS BEFORE INSTALLING ***

Seemed to presume a few things. First, it alphabetized my bookmarks (the ones carefully arranged in a specific order in my toolbar). Then, as I was fixing that, it just started rearranging them and creating duplicates.

I deleted all the changes and restored my backup. Might have been a conflict with Firefox Sync. Alas, we'll never know since Firefox is my primary browser and I trust open source over closed overall. In the end, I disabled iCloud sync in the Windows app and uninstalled the plug-in.