Rated 1 out of 5 stars
Seems broken with Firefox 29 and its new [*cough*/*splutter*] UI. Can only get to the options page with is a modal dialog. Frustrating as amongst a wealth of developer tools built in to Firefox, simply being able to view the HTTP headers ought to be a given, and all searching leads here, to a [*expletive*] dead end.
[Review is based on Mozilla failing to maintain compatibility, such that an apparently invaluable add-on no logner works, though also a reflection that it has not apparently been maintained for several years, and the help link is broken.]