You can use the Keyconfig or DOM Inspector extension and open the first Chrome window (File > Inspect Chrome Document).
Open the keyset (#mainKeyset) branch to see all the keyboard shortcuts that the DOM Inspector has found.

The Keyconfig extension can modify shortcut keys and also will show a list of curently assigned shortcut keys.

• DOM Inspector: https://addons.mozilla.org/firefox/addon/6622
• Keyconfig: http://mozilla.dorando.at/readme.html - http://kb.mozillazine.org/Keyconfig_extension

Thank you. Using DOM Inspector I looked through all the keys and found the culprit. It doesn't show how that key got set (e.g. which addon if it is an addon); ctrl-shift-h is set to the Show All History event but I don't see that in any of the default keyboard assignments. Not sure how, but at least I know where, and I suppose if I wanted to change I could use DOM Inspector. I do appreciate that I could see the keyboard assignments, but I found the interface a bit kludgey as I had to scroll to each different element to see the key assignment instead of a table, and I assume "accel" key is my ctrl key (I'm on Win XP with FF 3.6).

Keyconfig is PERFECT! Thank you so much for mentioning it. I can see all the key assignments, even sort by key assignment, and it's a breeze to modify. I'm not sure I "get" the different drop-down choices (the keystrokes they show surprise me, e.g. some of the key assignments that my addons create/provide don't show under the addons choice) but maybe one of these days I'll figure out.

Thanks again!

Im sorry to revive this, but i didnt want to create another topic for this. Anyway, is there a working version of keyconfig for FF4? Firefox 4 is almost released yet this addon isnt working and its a 'key feature' thats missing.