Hi Joop. i'll try to answer your points or get more info.
I copied all the user files from FF10 to a new directory which is used by FF17, but it seems that this FF won't use that. So how do I get all settings into the new one, including lists with sites, passwords etc.?
I hope that you are using the environment setting MOZILLA_HOME to store your profiles in one place outside of the programs directory. You should always back up your profile before trying a new version. You can go to the URL about:support and click the open directory button besides profile directory to find it.
Here's an article on moving your profile,
https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profileWhen having problems such as most you list, you should test in safe mode (Help-->Restart With Add-Ons Disabled) and also try a new profile (firefox.exe -profilemanager) to test if your problems are locally caused by corruption in your profile.
I can't get it into another language (that's something else than spelling, its about language toolbar, help etc). The nl.xpi from version 17.0.11esr is not accepted because its incompatible, the nl.xpi from version 17.0.10esr is accepted, can be installed, can be set to use it, but it doesn't make any difference, its English and it stays English.
Can you give me detailed instructions to reproduce this? I've never played with language packs. Also you should try with a new profile and also perhaps 17.0.5esr
The add-on container seems to run forever, had to do a ctrl-alt-del for popup and with the list and the kill option for deactivating the container.
This does seem to be a bug that I also see. Usually I can kill the Firefox process and start over.
If you use a master password and make use of passwords then on the background a proces is running, in popup it is "Inv.PM wachtwoord vereist" would translate like password required or something. With FF10 this closed as soon as you exit FF. With FF17 and FF24 it isn't closed and it sends the cpu meter to 99.99% with slow responces as a result. Same thing for if you want to install an add on. The manager keeps on running in the background and the cpu meter goes up to 99.99%
I can install add-ons without problems. I also just tested the master password thing, seemed to work fine.
Once again, create a new profile and see if you still have these problems and if you do you wil nee to migrate to a new one, see above URL