Rated 4 out of 5 stars

@BarbieGirl (May 27, 2014) - if you have some basic skill or confidence then switching to ctrl-right-click or other buttons, isn't hard. You need to change one line in each of two files of the extension. Back up your profile first "just in case" though. Quick "Howto", as I don't know your technical level:

1) Expand (unzip) -> modify -> rezip the extension, or set the preference "extensions.alwaysUnpack" to true in "about:config" before installing it. Both of these methods let you work with the extension's actual expanded files.

2) The files you want are "\bootstrap.js" and "\content\overlay.js". Both of these short files have a line that looks like this:
if (!e.shiftKey || e.button != 2) return;
Translation: if the shift key isn't pressed or the right button isn't pressed, ignore it. So you can make your change here. For example:

if (!e.ctrlKey || e.button != 2) return;
(uses ctrl-right-click, tested, works)
if (!e.shiftKey || !e.ctrlKey || e.button != 4)
(uses ctrl-shift middle - or wheel - button, probably works!)

3) Restart Firefox

This review is for a previous version of the add-on (0.0.6.1-signed). 

Rated 4 out of 5 stars

Very good tool, especially for studying Firefox's own chrome. Extension description should highlight this feature as it isn't at all obvious. So far the best tool I've found that lets you study firefox UI styling from within Firefox itself. Working for me with FF30+.

One issue (minor): after shift-right-click on some Firefox chrome, the Inspector's topmost bar (the > horizontal > bar > showing > the > style > hierarchy) can't be focused, it goes black or blanks out before you can mouse to it or use it. Apart from that, brilliant for studying and fixing chrome and UI issues!

This review is for a previous version of the add-on (0.0.6.1-signed).