As the official bearer of bad news, PWM 1.7.8b1 is reported as incompatible, and, although Ctrl+~ did work with Beta4, it does not work with Beta5, nor does PWM appear in the Tools menu.
To add to today's weird confusion with PaperPort, I thought that I had 1.78 installed in Beta4, but I realized that was not so, so I downloaded and installed 1.78, which is indicated as working through Beta6. When that did not work, I tried installing 1.78 in a new Firefox profile with no other extensions; still not Ctrl+~, nor anything in the Tools menu.
(How, after my previous, and incorrect, report about 1.78b1, I managed to get it to work with Beta4, I've quite lost track of. As for PaperPort, which I installed after installing Word Perfect Office X5 yesterday, I have found that one of PaperPort's components, nuanceWPS.exe, takes some 50% of the cpu, and even that, sometimes, when the .exe starts to run, it is impossible to kill the process though the Task Manager. Then there is the oddity that WP Beta4 stopped going to Add-ons a few days ago, and now Beta5 does not go there either--this may be due to a new add-on system being implemented, but I've seen nothing about such.)
Same problem with Beta 6: Ctrl+~ does not work, or Ctrl=`, I just tend to think about tildes, which must be some form of mania.