Hi Neal, According to an article I found, you have to install it manually from file. In the add-on manager (access it by ''Menu -> Add-ons'', or ''Ctrl+Shift+A'') click the cog icon, then select ''Install Add-on From File''. The XPI file itself should be under ''C:\Program Files (x86)\Adobe\Acrobat DC\Acrobat\Browser\WCFirefoxExtn\WebExtn\signed_extn'' (or maybe in the 64-bit ''Program Files'' folder). If this does not help, for further info refer to this thread: [https://community.adobe.com/t5/acrobat-discussions/mozilla-firefox-since-v127-0-cannot-install-anymore-the-adobe-acrobat-pro-xpi-extension/m-p/14894957] Regards, Balázs