The shortcut issue you describe appears to have been reported as bug 995756 a few years ago and even has a dupe, but there hasn’t been any recent activity for it. It should take little to have this fixed though; perhaps you can post a reply or vote in the bug, or we can ask for speeding up the fix.

The Menu Wizard add-on enables you to remap shortcut keys, but unfortunately it does not seem to be able to do so for the Scratchpad component.

If you really want a speedy fix for productivity or other reasons, you could open up the omni.ja file residing in the [drive:\]Program Files\Mozilla Firefox\browser folder (it’s a zip file, rename if needed), browse for the scratchpad.dtd file and replace the run.key entry with another non-conflicting one, such as "u". Then put that file in the zip file, rename it back to omni.ja and replace the original file that you should of course put aside as a backup. Note that this is about the omni file in the browser subfolder, not the one in the parent folder. I haven’t tested it but am sure it should work, at least with a Nightly zip version. Of course the omni.ja file will be overwritten with any Firefox update.

Side note: I assume you are aware of the fact Firebug will no longer be updated and you are advised to use Firefox Devtools instead?

Does this help?

If I use the DOM Inspector then I see no access keys for these buttons (these would be in the Scratchpad menu bar that isn't present), so it currently is not possible to use shortcut keys.

• view-source:chrome://devtools/content/scratchpad/scratchpad.xul

<toolbarbutton id="sp-toolbar-run"
               class="devtools-toolbarbutton"
               label="&run.label;"
               command="sp-cmd-run"/>