The venerable, vintage, and very useful, RequestPolicy add-on for Firefox now seems to be behaving erratically for me (and I know that I won't be able to use it for much longer in any case, when Firefox ESR moves to the next post-Quantum major release).
I am using RequestPolicy 0.5.28.1, and my Firefox ESR (on MacOS, if relevant) has recently updated to 52.8.1.
Now, RequestPolicy shows "Warning: Prefetch is enabled" in its menu, even though this does not appear to be the case in the RequestPolicy preferences. The "Disable prefetching" menu item takes you to a (not found) page on the RequestPolicy website.
In addition, the "Other origins within this page" submenu in RequestPolicy no longer opens.
RequestPolicy has served me very well, but it would appear that I now do definitely need to find a replacement addon.
I know that RequestPolicy Continued is under development, but it also does not appear to be compatible with Firefox Quantum. (I also did not install it previously as: original RequestPolicy still worked for me, RP-C was in a beta state, and I found its changed interface rather confusing.)
Are there any other Firefox addons that do essentially the same thing, namely: block all content from loading from other domains (or subdomains) unless expressly permitted?