After enabling account, when opening Tabslip in Android (2.3.6 Gingerbread) for the first time, in the broswer, when making the login, an error page with Forbidden (403): CSRF: verification failed. Request aborted. I'm therefore unable to use mobile app.

weird, i can't reproduce the problem, are you using the built in browser of android 2.3.4? (i have seen a ZTE-Blade in the logs - is that your device?)
maybe you could try to sign in right in the browser on tabsplit.net - is that working or do you have the same problem?

thanks for all the problem reports & suggestions, much appreciated, hope i can fix all asap

Used maxthron browser. Is ZTE Blade 2.3.4. Indeed was a browser problem. Hard to find if it was a problem in the app or in the browser. Tried google login (Open ID) and normal login. Changed the browser to normal one and was able to complete all the process. If no indication of error in your log, I can explore more is incompatibility with any third browser or just maxthron.

hmm.. i have just tried maxthron browser - the login dialog was a bit off the screen (grml) but i was able to log in.. do you have any additional addons, or have you disabled cookies or something like that? when i disable "allow cookies" in options -> privacy & security - i get the CSRF verification failed error message.. maybe this is what happened to you?

I am not able to login using the account provider option