I use 2 Yahoo calendars remotely via caldav to manage all my appointments in thunderbird (lightning plugin). My version of Thunderbird is 31.7.0 on Ubuntu Linux. This has always worked well but for a few weeks now (possibly since last Thunderbird update but not sure) I have been experiencing problems with meeting invites from Ooutlook accounts. If I accept an invite for 2pm, it will display in my thunderbird calendar as 3pm. Opening the event it will show "2pm UTC". It seems that the daylight saving hour is not applied. In contrast, setting up a new event myself in thunderbird doesn't cause this problem and the time is correctly recorded. The problem is not limited to invites from a single colleague but they are all from Outlook accounts. Logging into my Yahoo account, I can verify that my current location is correctly set. Strangely though, when I bring up the Yahoo web calendar, all events that come from my local thunderbird client are shown 13h ahead of the actual time, which can't even be a real time zone difference. Even weirder, those are then shown correctly again in my local thunderbird (on two different computers, work and home). It seems to me like there could be multiple issues here with the cross talk between Yahoo and thunderbird. Has anybody experienced the same problem? I'm running out of ideas for what else to try. Thanks for your help guys! I should probably add: my correct time zone is GMT (BST), i.e. UTC +1h