Allow use with local files (file:///) #32

Hi there, thanks for the great extension.

I noticed that this extension doesn't work with local files opened in the browser (i.e. file:/// rather than https://). I use a local html notebook (TiddlyWiki) a lot and it would be very useful to be able to use it in concert with this extension.

I appreciate that there may be technical limitations here, but I thought I'd ask.

Thanks again.