And Brave says it cannot open the zip file when I ask it to re-add the extension from the web store.
Hello! @Andy Flack
Welcome to the LastPass Community.
Unfortunately, we do not provide support for brave, it can be possible you were able to add the extension and used due to brave is base in chromium but if your check the article System requirements for LastPass , brave is not one of the options available.
We really want to help you and provide information about it but seems to be a problem with the browser.
Please let me know if you need additional help.
Greetings!
Verlaine | Customer Care