Comment 4 for bug 196493

I can reproduce this only with Mozilla's trunk Firefox (Minefield, I'm using the latest nightly)—and not with the Firefox packaged in Ubuntu.

I do recall seeing this bug quite a while ago (circa Edgy or Feisty) but I may have been using a Firefox build from Mozilla then as well.

My homepage is about:blank, and Firefox is set to show a blank page on startup.

Proper steps to reproduce:

1. Download, extract and run a Mozilla build of Firefox ( e.g. http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-trunk/ )
2. When prompted, make it the default browser (or do so from Edit → Preferences → Advanced → General); in my case, this sets the Web Browser command in System → Preferences → Preferred Applications → Internet to “/home/greg/firefox/firefox "%s"”
3. System → Preferences → Keyboard Shortcuts: assign a keyboard shortcut to “Launch web browser”; I have a specific “www” button, but I can also reproduce this using a “normal” key combination such as Ctrl+Alt+F
4. With Firefox closed, press the keyboard shortcut

Actual result: Firefox opens with the home folder's directory listing loaded (in my case, file:///home/greg/ )
Expected result: Firefox opens and shows whatever it's configured to show in Edit → Preferences → Main → Startup

5. With Firefox still open, press the keyboard shortcut again

Actual result: Firefox loads the home folder's directory listing into a new tab
Expected result: Firefox either opens a new blank tab, or opens a new window as if invoked from the Applications menu

Steps to then reproduce the expected behaviour:

6. System → Preferences → Preferred Applications → Internet: set Web Browser to (the in-built) Firefox; this sets the Web Browser command to “firefox %s” (it may be noteworthy that quotation marks are absent here, but not above)
7. With Firefox (both versions) closed, press the keyboard shortcut

Actual result: Firefox (in-built) opens, showing the “Welcome to Ubuntu Hardy Heron!” first-run page ( file:///usr/share/ubuntu-artwork/home/index.html ), as if Firefox had been invoked from the Applications menu
This is also the expected result

8. With Firefox (in-built) still open, press the keyboard shortcut again

Actual result: A new Firefox window opens, as if Firefox had been invoked from the Applications menu
This is the expected result

9. Close Firefox; press the keyboard shortcut yet again

Actual result: Firefox opens showing whatever is configured in Edit → Preferences → Main → Startup
This is the expected result

…

It seems that the problem *is* the pair of quotes I mentioned in step 6: changing “/home/greg/firefox/firefox "%s"” to “/home/greg/firefox/firefox %s” in System → Preferences → Preferred Applications → Internet after step 2 fixes this.

That means that this is a problem in the way that Mozilla's builds of Firefox set themselves as the default browser. (And probably not a problem in Ubuntu, though I still find it somewhat surprising that adding quotes would cause the home folder to be loaded.)

So, I've reported this to Mozilla: https://bugzilla.mozilla.org/show_bug.cgi?id=420408

Thanks for forcing me to investigate this properly :)