Hello all. I chose "Use Adobe Acrobat Reader" for open PDF in settings and it works fine until I closed Firefox and open it again. The setting bounce to "Open in Firefox". Then, I tried choosing "Always Ask", closing Firefox and opening Firefox again. The setting preserved as "Always Ask" and did not bounce to "Open in Firefox". I checked handler.json in user profile folder after I chose "Use Adobe Acrobat Reader" for PDF, action is 4: {"defaultHandlersVersion":{},"mimeTypes":{"application/pdf":{"action":4,"extensions":["pdf"],"handlers":[{"name":"AcroRd32.exe","path":"C:\\Program Files (x86)\\Adobe\\Acrobat Reader DC\\Reader\\AcroRd32.exe"}]}},"schemes":{}} But then after restarting Firefox, it changed to 3: {"defaultHandlersVersion":{},"mimeTypes":{"application/pdf":{"action":3,"extensions":["pdf"],"handlers":[{"name":"AcroRd32.exe","path":"C:\\Program Files (x86)\\Adobe\\Acrobat Reader DC\\Reader\\AcroRd32.exe"}]}},"schemes":{}} Checked handler.json with "Always ask". Before and after restarting Firefox, action is 1, which is expected and correct. Some other colleagues reported the same issues as well. I am thinking if this is a bug from Firefox. Some more notes here: * The issue only happens to PDF, for other Content types, all good. * Already disabled all plug-ins and extensions. * Tried refreshing Firefox in safe mode * Tried choosing another external PDF reader Foxit * Firefox version is 140.0.2 Some screenshots are attached showing where it is. Hope someone can help on it. Thanks in advance.