I had an add-on downloaded and running before the last update (Firefox Quantum version 67.0 (32-bit)). It disappeared, so I tried to load it again, but I get the error message: “Firefox prevented this
site from asking you to install software on your computer”
It doesn’t though. I have tried several times. I tried restarting Firefox and even rebooted my pc. It will not load. Is there something else I could do?
In the top right you have a cog/gear () button, clicking that will give you a drop down menu. That menu should have an item “Install Add-on from File…”.
It doesn’t download a file. On the page www.mypoints,com I select "add Score to Firefox. It opens a new tab (https://www.mypoints.com/install/mypoints_score.xpi) and without doing anything (blank screen) I get that error message saying I can’t install software.
(sorry to be such a pain)
I think I see the problem. I scrolled down on https://www.mypoints.com/download-score to where it says “Add to Firefox” and clicked that button. That directs an XPI link to a new tab, which Firefox apparently doesn’t allow.
If I manually modify the link in the Page Inspector tool to remove the target="_blank" attribute (the bit of code that sends the link to a new tab), then it works normally: I get a warning, I click Allow, then the installation drop-down appears.
As an alternate workaround, instead of hacking the page’s HTML, you can right-click the button and Save Link As to save the XPI file locally. Then you can use the method Martin described to load that locally saved file.