Added: Compatibility for e10s (i.e. multi-process Firefox).
While there are few user-visible changes there are a lot of changes under the hood: Highlighting is now done in a separate CPU thread which should greatly increase perceived performance (i.e. no more delays / UI freezes during the few milliseconds it takes SearchWP to highlight matches on the page). As soon as e10s will be fully enabled by Mozilla (e10s will be enabled gradually for users starting with Firefox 49) you'll be able to profit from the full potential of this change.