You should rather use Privoxy and AdBlock-plus instead of Ghostery, those are free and open-source solutions, not proprietary.
I use the Firefox-build from mozilla.debian.net/experimental, but it does not deliver the latest version 29 yet.

I also have many tabs open (usually around 30-60) and the feature I miss from FF/TMP was to have 3-4 rows of tabs. I have my screen in portrait mode, so the additional vertical use of real estate is OK for me.

Chrome doesn't support this and so I am stuck with navigating 'blind' although the "new tab after current tab" behaviour (which I hated) helps to maintain some kind of locality in tab navigation.

I've seen the "must restart" issues with upgrades in the past, but I ruled that out pretty early.

As you say it probably makes sense to pick a release and stick to it. Right now my sources-list just reads:

deb http://mozilla.debian.net/ wheezy-backports iceweasel-release

Which seems like a safe choice, but I might have to revisit. I guess the plus side of this "fun" experience is that my history is truncated, I have only three addons loaded, no support for flash, and things seem fast again.

Happily I store my bookmarks under revision control so I lost nothing of note..

Stay with the Firefox/Iceweasel ESR releases? That way new bugs, compatibility-breaking changes and confusing UI redesigns only happen once year, instead of once a month.

I'm tempted to go back to Iceape's very familiar UI (last version in archives.debian.org was based on FF10), built with hardening options, and maybe backported security fixes (especially for the nasty JavaScript race that some agency exploited against Tor users), and I'd be using NoScript most of the time anyway. Possibly even run it under another user ID.

p.s. Firefox/Iceweasel on GNU/Linux doesn't upgrade cleanly; you have to close all windows and restart or weird things may happen in the UI.

Fixed - Though I have no idea how.

I purged everything, reinstalled, and there was no change.

So I figured I'd stick to the mozilla-provided binaries to simplify things. I downloaded version firefox-28.0.tar.bz2 and that allowed me to install addons. Once I'd installed "tree-style-tabs" then running firefox 29.0.1 was then able to install a new addon ("adblock+", FWIW).

Now I've purged everything binary from mozilla, reinstalled the wheezy-backport packages, and add-on installation continues to work. It looks like the first addon did something magic to allow later ones to work.

Either that or I did something wrong in a past life.

Cookies are probably a good idea, thanks. I'll look into it.

I really really really want firefox back - having vertical tabs is so much nicer when you have 20+ open at a time, as I often do.

I switched to Chrome mainly because I was forced to use it in my Chromebook and then found the sync between phone, CB and main computer useful.

I hated not having tabmixplus, but got used to the Chrome way now. Truncated urls etc. still bother me, but I find it usable.

P.S. any chance of getting cookies to store the name/email/website for the comment form? ;)

Going down the list of replies - thanks to all of you!

I had checked that there were no firefox processes running before each step.

Strace shows nothing obvious wrong at any point.

$ dpkg -S /usr/share/mozilla 
iceweasel: /usr/share/mozilla

Interestingly the same problem occurs with a brand new user - and just for completeness this error occurs regardless of the extension, it isn't just ghostery that fails.

Using safe-mode seems to disable addons completely, but doesn't solve the problem.

Running with NSPR_LOG_MODULES=all:5 shows nothing obvious wrong either, certainly nothing happens that looks different between the point I click "Add to firefox" and give up.

No other package updates that seem relavent have been applied recently:</p.

shelob ~ $ grep ' install ' /var/log/dpkg.log
2014-05-03 01:13:48 install xulrunner-29:amd64 <none> 29.0-1~bpo70+1
2014-05-03 13:01:16 install libsvga1:amd64 <none> 1:1.4.3-33
2014-05-03 13:01:17 install mplayer:amd64 <none> 2:1.0~rc4.dfsg1+svn34540-1+b2
2014-05-03 13:01:18 install mencoder:amd64 <none> 2:1.0~rc4.dfsg1+svn34540-1+b2
2014-05-04 14:13:01 install libllvm3.0:amd64 <none> 3.0-10
2014-05-04 14:13:02 install g++-4.6:amd64 <none> 4.6.3-14
2014-05-04 14:13:03 install libstdc++6-4.6-dev:amd64 <none> 4.6.3-14
2014-05-04 14:13:04 install libclang-common-dev:amd64 <none> 1:3.0-6.2
2014-05-04 14:13:05 install clang:amd64 <none> 1:3.0-6.2
2014-05-04 14:13:05 install libffi-dev:amd64 <none> 3.0.10-3
2014-05-04 14:13:06 install llvm-3.0-runtime:amd64 <none> 3.0-10
2014-05-04 14:13:07 install llvm-3.0:amd64 <none> 3.0-10
2014-05-04 14:13:07 install llvm-3.0-dev:amd64 <none> 3.0-10
2014-05-05 21:56:00 install mtools:amd64 <none> 4.0.17-1
2014-05-11 10:50:14 install dh-autoreconf:all <none> 7
2014-05-12 10:07:11 install lua-socket:amd64 <none> 2.0.2-8
2014-05-19 15:40:50 install vorbis-tools:amd64 <none> 1.4.0-1
2014-05-21 09:18:23 install gparted:amd64 <none> 0.12.1-2+b1
2014-05-21 14:30:22 install nfs-kernel-server:amd64 <none> 1:1.2.6-4

"Moving ~/.cache/mozilla and ~/.mozilla out of the way don't help"

Something is very wrong in your installation o.O

I have the same problem under CentOS.

My general troubleshooting on this is:

1) Create a new user. Does this user get the same problems?
2) What other libraries were updated around the time this started though the /opt/firefox should avoid most of them
3) Does booting into a livecd and using your environment cause the problem to still occur?

- Check the error console (menu, developer, browser console) and check if there are any interesting notes there.
- Try running iceweasel/firefox with -safe-mode
- Try running iceweasel/firefox with NSPR_LOG_MODULES=all:5 and see if that yields something interesting.

dpkg -S /usr/share/mozilla ; anything in that list other than iceweasel itself?

> "Ghostery could not be installed because firefox cannot modify the needed file".

Check "ps auxf" and make sure no instance of iceweasel/firefox is running. After doing so, try strace -f again, and look for errors?

"which-pkg-broke iceweasel"?

FWIW when I click "Install now" on a plugin it seems to do nothing. When I open up the extensions menu I see a progress bar that never updates - and when I restart the browser the extension list is empty once again.