On my new laptop (Windows 8), Thunderbird runs very slowly, fails to show many incoming emails, and frequently becomes unusable.

I now have two Windows 8 laptops, but I have installed Thunderbird on only one of them (an Acer). It has given continual problems. It is very slow retrieving and deleting messages; it frequently crashes; and when I compare the Thunderbird inbox with my webmail inbox, it is clear that many incoming messages fail to show up on Thunderbird. I tried uninstalling and reinstalling, but this made no difference. I have had no problems on this machine with other programs, and no problems with Thunderbird on Windows 7 machines.