But... Rated 3 out of 5 stars
..github is a collaboration hub for developers, and I need to sign up for it. I'm just a normal joe who wants to report issues so this app gets better. Why not just provide a gmail address? Or I can simply tell you my experiences here...there are two, one involving non appearance of 'highlight this' menu option when viewing a framed page, and the other involving random, automatic extra highlighting of links associated with highlighted text on a wikipedia page.(I'm surprised Mozilla don't provide a facility for this)This review is for a previous version of the add-on (initial.rev362). This user has other reviews of this add-on.
I have observed non-appearance of context menu item 'highlight this' when I press the right mouse button prior to completion of page load. The 'contentScriptWhen' property of the menu item is set to "start" so it should be available from the start of loading (as is the "Select color highlighter" widget in the lower right corner) but for reasons I haven't yet figured out, still waits for page loading to complete. Is it failing on framed pages when it says "done" in the lower left corner and/or the orange clockwise-spinning ring in the tab header has stopped spinning? A URL in which it is failing might be helpful.
I'm aware of some issues with Wikipedia. The most recent revision, "Version initial.rev438" should help with some of them. It is still awaiting Preliminary Review from addons.mozilla.org, but you should be able to download it at https://builder.addons.mozilla.org/xpi/prepare_download/1046583/revision/439/