mail.proton.me - see bug description

[2004seraph]

URL: https://mail.proton.me/u/0/all-sent/3hpQ1IQ_1012292vVH4iD6s-MODQtPaxPTlUUby5JgidSUbnXiVvJDotfyYCKGYXeTs2kRxhAbnMGSoSq3OSiw==/U9h9HqZd93EaeXwn2_yDOdYMNIEUuVPdZYQH9sXfg3mbrPWylP34TzQki2rU495gRFf9nqg_hhrT_aE_bci_WA==

Browser / Version: Firefox 133.0
Operating System: Windows 10
Tested Another Browser: Yes Chrome

Problem type: Something else
Description: Only offers to install url provider for "mailto:" links on chrome, not firefox (which does support it)
Steps to Reproduce:
When loading my inbox for ProtonMail on Firefox, the application does not offer to install a "mailto:" link URL handler in my browser. But if I use the "Chrome Mask" extension to convince the website I'm using Chrome, Firefox shows a banner (not the app) to install its URL handler.

Browser Configuration

• None

From webcompat.com with ❤️

[2004seraph]

Here is a screenshot of my preferences after I was able to install the handler, I did not capture one of the original banner shown above ProtonMail:

View the screenshot