You can find more on the status of e10s and a11y on https://wiki.mozilla.org/Electrolysis/Accessibility.
The way you phrase your question, does you add-on depend on electrolysis? Does your addon require accessibility?
Maybe you just misread the "all add-ons" piece? What that sentence means is that we generally have e10s on, but there are a few reasons to switch it off for some of our users.
We're currently testing if 51 is a good release to stop switching off e10s when add-ons are detected. (There's already a whitelist where we keep e10s on if you only have add-ons on that list.)
Regardless of add-ons, we switch e10s off if a11y got detected. The details of when and platforms are on the wiki, and also that there might be false positives. That doesn't mean that we're switching off add-ons in that case. Add-ons just work, a11y just works, but these users don't have e10s on.