I've just done a clean install of Mint13MATE (it's configurable !! - and with none of this tasbar-across-the-top-of-the-screen Gnome3 rubbish) after using and enjoying Mint12 for a few weeks and I used the excellent Backup/Restore tool that's in both 12 and 13 to save/restore my (Mint12) /home directory and installed packages.

Unfortunately/stupidly I saved the archive and software list into an ntfs partition - in spite of reading the warnings about permissions etc not being saved/restored when using ntfs. So a fair bit of fiddling around with permissions etc has been needed .

But there is one annoying small problem with Firefox: when the restore from the saved12 > 13 was done all my old tabs etc restored perfectly to my amazement/delight - but at some stage since then the bookmarks and history parts of Firefox (which updated itself to 14) have stopped working - blank screens show up in both history and bookmarks - it won't create any bookmarks, isn't saving the "History", and it won't even import an html of all my old bookmarks. But it will "restore previous session OK" - hence this slight Edit which I've just done.
I did have to do quite a bit of fiddling around with AdditionalDrivers/jockey (which didn't work!) and the proprietary ATI driver from the AMD site [..8...run] installer to get my Radeon vidcard driver installed/working again - even had to use the --force option because some library (that I couldn't find anywhere) wasn't present - so maybe something might have been corrupted during that process?
The basics of Firefox are working OK - hence writing this! - but the titlebar/header seems very "reduced" and, as I say, it has no History or Bookmarks functionality. But it will "Restore previous session" OK!

I tried to uninstall Ffox and reinstall it - but apparently one can't do that - it seems that there has to be one browser app present in the OS.
I guess I could install another browser and then do the uninstall/reinstall on Ffox - or maybe just start again with another clean install of Mint13 and be very careful about not upgrading Ffox - and removing it from the installed software list and not doing an "automatic upgrade of everything" - ie leave the older Ffox that came with the install .iso of 13Mate.
But having spent a few hours of getting everything set up the way I like it - editing Grub, colours, root passwwd etc etc I'd prefer to keep it all as it now is!

So I thought that before doing either of this/these (FFox reinstall or whole OS wipe/reinstall) it might be worth putting a question here to see if any upline has an idea about how to fix this problem.

TIA
PaulW

In good opensource/copyleft spirit :-) I'll post the solution that I eventually found for this problem - in case others have similar issues - and quite a few others are having similar troubles, it seems! - before marking my original question as "Solved".

I had to steel myself to upgrade to Mint13 - unlucky number etc - but eventually decided to do so because of its Long Term Support aspect - and because I'd been enjoying the Mint12 version so much for a few weeks!

So:
(1) Deciding/realizing/confirming that I had a "corrupt" install:
There were no responses to my query - maybe there's not so much "foot traffic" on the LQ Mint Distro forum??
Besides the small-ish Firefox problem, which was really "the canary in the coalmine", there were a few other indicators that something was not quite right with my Mint13Mate64bit install.
I had had to use the --force option to get the vidcard driver installed from a [ ...run] downloaded ATI file - when jockey didn't work. But, after doing this (warned as not advisable), the ATI Radeon Catalyst GUI control app would often not open at all, or maybe take a very long time to open - even from a root GUI (a not-advisable practice, so I'm told!). And then it would occasionally "hang"/blackscreen and would only run at ridiculous "fixed" settings - eg 4000x2400, 180Hz refresh etc etc! - which could not be altered - even from root.
And then the "Suspend" shutdown option would suspend OK - but then only give a grey screen on Restore - = reboot needed.
Also the OS's general responsiveness was quite "sluggish" and trying to "drag" open windows across the screen produced some quite "stuttering"/smeared effects.
So with Firefox and the vidcard setup not working correctly, it became fairly clear that the OSinstall was somewhat "corrupt" and obviously needed re-installation.

(2) I "wiped" (using Disc Eraser (and partition ditto!) in the PartedMagic bootable CD) the 50G partition I'd installed onto.
Yes, I've been told that this is not strictly necessary, but it only takes 10 minutes or so - and, I think, does prevent a few odd inexplicable "glitches".
Then I did a "clean" (re)install offof the Mint13Mate64bit ISO DVD - and used the AdditionalDrivers/jockey app to download/install the proprietary ATI vidcard driver - and checked that Ffox was running AOK - which it was.
I then "Restore"d my files and software using the two parts of the Backup/Restore app - to find that the same "no Bookmarks & History" problem was happening again .

(3) So I redid the whole wiping/clean-reinstall process again - but decided to be a little more cautious about the "recovery" of my old Mint12 (LMDE) files and installed software!
Again I downloaded/installed the "basic" ATI vidcard driver - using AdditionalDrivers/jockey - now working AOK for me. I haven't been brave enough! to try the "post-release updates" version yet ! - because it did "hang"/corrupt an installed&working "basic" driver at one stage in this rather tortuous process!
And checked that it was working OK - and correctly recognizing my "vintage" Philips LCD monitor and its ancient resolution (=1280x1024@60Hz - with about a half-second response time!) - which it was!
Then checked that the installed Ffox14 was all working OK - which it was too!
>>> Then, when copying/re-installing all the Mint12 files, I changed the "overwrite" setting from its "default" of "Checksum mismatch" to "Never" - in order, so I figured (correctly, it seems!), to not overwrite the existing Ffox files/caches/install etc with their older Firefox(10?) equivalents - pleasant though it had been to see all my old tabs etc "copied across" from Mint12 > Mint13.
After this checked that Ffox was still all working OK - which it now was/is!
And then ran the "Restore software" part of the app - which gave a screenful of non-functional "text"-ish icons.
And then re-ran the "Restore files " and "Restore software" parts of Backup/Restore once or twice again - which, eventually, gave correct icons and app functionality restoration - apart from (my preferred/"normal") Gedit basictexteditor which has now defaulted to Pluma in the Mate GUI/desktop and needed downloading/re-installation.

So I now have an excellent (mostly)fully-functional Mint13MateLTS&Firefox14 OS/browser install - which is to my delight (+/- here and there) mostly as good/functional an OS as winDoze7, IMO!
And, being Gnome2 it is fully configurable :-)
So hopefully I won't have to go through all this slightlycomplex/tedious/"tricky" process again for a while - but at least I now know how to do it!

I would humbly suggest that possibly the "default setting" for the "Overwrite" option in the "Backup/Restore Files/Software" app might perhaps be better set as "Never".
Or, at least, that users of this excellent/useful Backup/Restore app, in a generally excellent 64bit ripper of an OS, should consider quite carefully how to use it - as the title of this posting says!

Paul W