Rated 5 out of 5 stars
Sorry to post this here, but I couldn't find any e-mail address or anything else to contact you directly.
I've just uploaded a new version 1.4.10 of FindBar Tweak which will fix the placement of the findbar (the issue from the previous user review), it's currently in the review queue, I suggest you use that version when you work on these compatibility issues. It was a problem that could possibly affect other themes as well, so I fixed it within the add-on itself.
To make sure your theme stays compatible, you can remove the findbar[movetotop] margin-top entries you added in your stylesheets, they won't work anymore with the new FBT version (I mean, they work but they're irrelevant, as the add-on now ignores those now).
Also, if you want you can go to https://github.com/Quicksaver/FindBar-Tweak/issues/22 for a detailed explanation on how to change the color of the find bar and its corners when it's moved to the top, so it fits better your theme (this I can't do from within the add-on itself, sorry).
FXChrome is a pretty cool theme, I'd like to make sure my add-on stays compatible with it, so let me know if you need anything else or if any new issues between the two arise!