With the latest edition of Firefox, they have integrated the Pocket "reader", which when activated will load a "reading" version of the original page at an URL like about:reader?....
However user scripts are not allowed for about pages, including the about:reader.
I've made a small hack in modules/util/isGreasemonkeyable.js, by adding a line like the one below just after if (/^about:blank/.test(url)) return true;:
if (/^about:blank/.test(url)) return true;
if (/^about:reader(\?.*)?$/.test(url)) return true;
I'll bet dollars to donuts that like other about: pages, it has chrome privileges, so it will never be greaseable.
I didn't say (although I wanted to) in my initial comment that I have zero knowledge about what my update implied. Perhaps it just opened a large security whole in my browser, but since I use only user scripts written by me, I am less concerned with potential security issues from my own scripts.
But, indeed a more knowledgeable person, in the inner workings of both Firefox and Grease Monkey, should look into this.
What exactly are the steps to launch such an about:reader page? I couldn't figure it out in the ~2 minutes I spent trying.
For example open the following link, and in the address bar, at the right, just before the reload button there is a small button like a book. Just press it.
(I guess you need the latest Firefox 38.0, and this feature works only on some pages like the one above.)
Oh, no about: shows in the UI in that case. But I'm clear what you're talking about and I can check what that context is.
Indeed the address bar still shows the original URL, but if you run inside the console document.URL, something like about:reader?... appears.
(I applied the patch described in the first comment and it works.)
Allow scripts at `about:reader`.
This should be in 3.5beta1; let me know what you think:
Perfect. Works like a charm for reader URL's.