Reviewing just the developer docs (not counting undocumented bugs), here's
stuff that needs a closer look for each FF version.

FF24: 
  - Seems fine.
FF23:
  - Mixed content blocking will need to be fixed or disabled.
FF22:
  - WebRTC is on by default
  - Clipboard data:
    https://developer.mozilla.org/en-US/docs/Web/API/ClipboardEvent.clipboardData
  - Web Notifications may cause proxy issues if they contain embedded
    URLs/content?
    https://developer.mozilla.org/en-US/docs/WebAPI/Using_Web_Notifications
  - Blob uris/objects may require caching isolation equivalent to data uris
    https://developer.mozilla.org/en-US/docs/Web/API/Blob
  - Is the new third party cookie blocker better or worse?
    https://blog.mozilla.org/privacy/2013/02/25/firefox-getting-smarter-about-third-party-cookies/
    http://webpolicy.org/2013/02/22/the-new-firefox-cookie-policy/
FF21:
  - No major issues
FF20:
  - Probably fine:
    https://developer.mozilla.org/en-US/docs/Web/API/Navigator.getUserMedia
FF19:
  - New canvas methods toBlob(), isPointInStroke():
    https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D
    https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement
  - File can return "current" date when time is unknown (verify no timezone
    leaks, etc)
    https://developer.mozilla.org/en-US/docs/Web/API/File
  - https://developer.mozilla.org/en-US/docs/Web/API/CSSPageRule
FF18:
  - https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe#attr-allowfullscreen
  - https://bugzilla.mozilla.org/show_bug.cgi?id=767818 (navigator.mozPay??)
  - https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Proxy
  - https://developer.mozilla.org/en-US/docs/Web/Guide/User_experience/Using_the_Page_Visibility_API
  - https://hacks.mozilla.org/2012/10/aurora-18-hidpi-touch-events/


And here's the list of undocumented bugs that need a closer look:

FF24:
 https://bugzilla.mozilla.org/show_bug.cgi?id=855741
 https://bugzilla.mozilla.org/show_bug.cgi?id=549861
 https://bugzilla.mozilla.org/show_bug.cgi?id=858234
FF23:
 https://bugzilla.mozilla.org/show_bug.cgi?id=525444
 https://bugzilla.mozilla.org/show_bug.cgi?id=769871
 https://bugzilla.mozilla.org/show_bug.cgi?id=811403
 https://bugzilla.mozilla.org/show_bug.cgi?id=818675
 https://bugzilla.mozilla.org/show_bug.cgi?id=834835
FF22:
 https://bugzilla.mozilla.org/show_bug.cgi?id=845010
 https://bugzilla.mozilla.org/show_bug.cgi?id=783129
FF21:
 https://bugzilla.mozilla.org/show_bug.cgi?id=834595
 https://bugzilla.mozilla.org/show_bug.cgi?id=823175
FF20:
 https://bugzilla.mozilla.org/show_bug.cgi?id=776443
 https://bugzilla.mozilla.org/show_bug.cgi?id=815743
 https://bugzilla.mozilla.org/show_bug.cgi?id=818800
 https://bugzilla.mozilla.org/show_bug.cgi?id=770844
 https://bugzilla.mozilla.org/show_bug.cgi?id=764240
 https://bugzilla.mozilla.org/show_bug.cgi?id=617532
 https://bugzilla.mozilla.org/show_bug.cgi?id=789932
FF19:
 https://bugzilla.mozilla.org/show_bug.cgi?id=801576
 https://bugzilla.mozilla.org/show_bug.cgi?id=804944
 https://bugzilla.mozilla.org/show_bug.cgi?id=722979
 https://bugzilla.mozilla.org/show_bug.cgi?id=723002
 https://bugzilla.mozilla.org/show_bug.cgi?id=723005
 https://bugzilla.mozilla.org/show_bug.cgi?id=648610
 https://bugzilla.mozilla.org/show_bug.cgi?id=801402
FF18:
 https://bugzilla.mozilla.org/show_bug.cgi?id=745025
 https://bugzilla.mozilla.org/show_bug.cgi?id=750862
 https://bugzilla.mozilla.org/show_bug.cgi?id=790946
 https://bugzilla.mozilla.org/show_bug.cgi?id=782453
 https://bugzilla.mozilla.org/show_bug.cgi?id=774963
 https://bugzilla.mozilla.org/show_bug.cgi?id=737003
 https://bugzilla.mozilla.org/show_bug.cgi?id=726615
 https://bugzilla.mozilla.org/show_bug.cgi?id=783531
 https://bugzilla.mozilla.org/show_bug.cgi?id=722861
 https://bugzilla.mozilla.org/show_bug.cgi?id=796523
 https://bugzilla.mozilla.org/show_bug.cgi?id=564815
 https://bugzilla.mozilla.org/show_bug.cgi?id=769764
 https://bugzilla.mozilla.org/show_bug.cgi?id=769569
 https://bugzilla.mozilla.org/show_bug.cgi?id=787931
 https://bugzilla.mozilla.org/show_bug.cgi?id=695399
 https://bugzilla.mozilla.org/show_bug.cgi?id=791019

-------------------------------------------------------------------

Canvas patch review:
 https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement
  + toDataURL (patched to return white)
  + toBlob (patched to return white)
  + toDataURLHD (unimplementd)
  + toBlobHD (unimplemented)
  + mozGetAsFile (patched to return white)
  + mozFetchAsStream (chromeonly)
 https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D
  + getImageData (patched to return white)


Test cases needed for proxy bypass and info leak to/from OS:
 https://developer.mozilla.org/en-US/docs/Web/API/ClipboardEvent.clipboardData
 https://developer.mozilla.org/en-US/docs/WebAPI/Using_Web_Notifications
 https://bugzilla.mozilla.org/show_bug.cgi?id=767818 (navigator.mozPay)


Bugs that need deep review:
 https://bugzilla.mozilla.org/show_bug.cgi?id=549861 (font-variant probing)
  - Should we limit this?
  - http://dev.w3.org/csswg/css-fonts/#font-rend-props
 https://bugzilla.mozilla.org/show_bug.cgi?id=858234 (execute after DL)
 https://bugzilla.mozilla.org/show_bug.cgi?id=789932 (move extenal app launcher to alt thread)
  - Does the external-app-blocker still prompt?


Bugs filed:
 - Fingerprinting:
   https://trac.torproject.org/projects/tor/ticket/10284
   https://trac.torproject.org/projects/tor/ticket/10283
   https://trac.torproject.org/projects/tor/ticket/10286
   https://trac.torproject.org/projects/tor/ticket/10285

