I've been using MBAE Beta 220.127.116.11 for quite some time with no ill effects. Lately, however, I started experiencing a problem with Firefox. Sites would not open in new tabs, whether I opened a tab first and used a bookmark or typed in an URL or right-clicked on a link and selected "Open in new tab." This behavior was erratic -- sometimes sites would open and sometimes they would not, but mostly, sites would just not open.
I tried the usual Firefox troubleshooting: started in FF Safe Mode; uninstalled all add-ons; cleared cache and cookies; refreshed FF; uninstalled FF and downloaded and installed a new copy. Nothing worked until I realized that although MBAE is not an "add-on" per se, it was starting with Firefox, even in FF Safe Mode.
I disabled MBAE and the problem seems to have gone away, although it's been less than a day and I'm still testing.
I don't know exactly when this behavior started, but it's currently happening with Firefox 58.0.2 (64) running on Windows 7 Pro x64 (uptodate with all Windows Update patches).