FWIW: Pale Moon and Roboform
I'm assuming you already read these instructions and had no luck. (Also see the last 2 posts on the 2nd page)
In a different thread the following month, the same developer states:
'Roboform has always been a problem, and the Roboform developers simply refuse to provide support for Pale Moon. A few people have been able to get it to work in the past by using a "lite" version .XPI but no guarantees that that works or will continue to work. Roboform's refusal to support Pale Moon or to even provide support for getting it to work in Pale Moon has been a thorn in quite a few users' sides - especially with the growing popularity of this browser, and more and more third party tools including Pale Moon support, they may actually be looking at losing paying customers.
Most compatibility issues there are with add-ons are the result of one or more of the following: ..'
Sorry I don't have anything more constructive to add.