Thunderbird seems to be blocking most of my web links. Those it doesn't block never resolve

Hi: I'm fairly new to Thunderbird-I've only been using it for a few months. For the first while, everything was working fine. Now, almost all links in emails don't even open a browser window. Those rare ones that do open a browser window never seem to resolve or draw a page. I don't remember changing any security settings from the defaults. What should I check to prevent this? I'm savvy enough to know what to click on, and what not to. Thanks in advance