After upgrading my Debian testing yesterday, I had the bad surprise to see that I couldn't read my emails anymore. I'm using Icedove (aka the unbranded Thunderbird available in Debian) and the software couldn't start anymore.
After a bit of searching, the solution happens to be quite simple. I've summarized the information I found here, in the hope that it may save time for others...
The cause : incompatibility with the Lightning calendar extension
Investigating the issue, I tried to launch Icedove from the command line :
icedove: relocation error: /home/pierre/.icedove/<span style="color: #3366ff;">my_profile_dir</span>/
version xul24 not defined in file libxul.so with link time reference
Searching the web, this bug was in fact reported a few months ago and is due to me using the Lightning calendar extension from Mozilla.
One message by Carsten Schoenert points specifically to the incompatibility :
if you using lightning from Mozilla this issue is normal. The symbol tables are incompatible between Icedove/libxul and upstream lightning. Please use iceowl-extension instead. The lightning package wan't work with the Icedove packages.
And the solution seems to be : use the iceowl extension instead.
But one question remains: how to fix my email client ? How can I remove the incompatible Lightning extension if icedove doesn't start ?
The solution : removing the extension using "Safe Mode"
It happens that removing this extension was easy enough by launching icedove in Safe Mode, which disables all extensions. I had never used it, but it is easy to do from the command line :
$ icedove -safe-mode
Then, I could simply remove the Lightning extension using the regular add-ons management tab.
Now, restarting Icedove "normally", it just works!
I'll still have to investigate the replacement solution of using iceowl extension. But since I haven't been using the Lightning calendar much for some time, I'll probably leave it like that...