Dell XPS 8930, Solid-state C drive and 1 TB D hard-drive, Windows 10 - updates current, Firefox recently updated to 85.0. Since the update to 85.0 operations in some areas are different, but I was able to restore actions back to how I preferred. One action causing me grief I haven't been able to resolve is actions involving pdf files attached to an email. I left-click on the attachment download arrow and choices are presented (normal). If I select "open with Adobe Acrobat" a box appears stating "There was an error opening this document. This file is already open or in use by another application" (I didn't open it and I didn't initiate another App) and the file doesn't open. If I choose "Open with Firefox" a window opens with "file:///C:/Users/metzg/AppData/Local/Temp/Invoice-1.pdf" in the Address bar, but nothing else happens. If I click the address and click on the address that appears below with " - Visit" added to it the file opens successfully. If I choose "Download" the pdf file appears in the Download location and will then open normally. I prefer most often to just open the pdf file directly in Adobe Acrobat and save, print, or take another action of my choice. Since the update to 85.0 this problem has been an issue. I have searched Firefox help and haven't found solutions that specifically address this issue. I have tried changing the settings in options, closing Firefox, opening Firefox and changing back to "Always Ask" and the issue persists. If someone else has experienced and resolved this issue I would appreciate info on how you accomplished a solution!