Hello ThaiED, The reason it changed may be because you selected "Always open pdf with this". Just simply change your default pdf reader again and the next time you open a pdf, change the app you are using. Tell me if that helped and Stay Safe!

Change it many times it can stay as default in the setup but others can open it  ; they override. In my task menu I have wps viewer as it opens itself and when ever there is a download; it asks to open it in its own windows on bottom right. ITs a "wps office program trying to open my pdf. How can those programs even be allowed to popup to offer to open a file ?

How can those programs even be allowed to popup to offer to open a file ?

Good question, I'm not completely sure about that but I'll keep researching about it. It probably has something to do with Windows.

Hi ThaiED, could you explain this part or illustrate what it looks like with a screenshot:

In my task menu I have wps viewer as it opens itself and when ever there is a download; it asks to open it in its own windows on bottom right.

That sounds like something different than the normal Firefox download dialog.

I think you have already checked, but just in case, what do you have on the Options page for "Portable Document Format" files: Preview in Firefox, Use Foxit, or something else? This article has the steps to get to that setting: View PDF files using Firefox’s built-in viewer.

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One possible culprit for odd handling of downloads would be an extension. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove).

Any improvement?

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Finally, your Firefox identified itself as version 59, which is no longer supported. Can you update to a current version?

• Regular release: Firefox 76.0.1 -- Update Firefox to the latest release
• Extended Support Release of Firefox 68 -- Switch to Firefox Extended Support Release (ESR) for personal use