The very best search addon in the world Rated 5 out of 5 stars

Congratulations, dude!

I'm afraid there are still compatibility issues even with Version 3.39.2 and e10s manually enabled, and all other addons disabled: I still cannot export/import searches, and the right click to preview in Smart Searchbox does not open the preview panel either (Switching to "Default preview" does nothing either). As soon as I manually disable e10s, they both work perfectly. (W8.1x64 and FF49.0.2)

Could you please look at it?

Yes. FS doesn't support e10s. It'll take a while b4 I release an e10s version. It's a big big rewrite unfortunately...