Can you open the links if you paste them in the location/address bar or does this fail as well?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Hi! Yes, I can open links in another browsers what I cannot open in the Firefox; therefore, I always jumping between browsers. I see the same situation in Android version as well. I will check Firefox as soon as I will have again trouble to open a link in Firefox.

I've had this situation again, I started Firefox in the Safe Mode and it didn't help. I cleaned cookies and cache, restarted and the problem still exists. I have the same problem (cannot open some of my favorites links) at Firefox on my mobile (Android) devices as well.

It seems to me I found the solution ;) It's from here https://support.mozilla.org/en-US/questions/1039902

    Go to setting (3 bars) > options > applications.
   Under applications panel.
   Find Portable Document Format (PDF) in the list and click on it to select it.
   Click on the drop-down arrow in the Action column for the above entry and select Use PDF reader name (in Firefox) or preview in firefox. 

I've choose "Preview in Firefox"

Any suggestions how I can fix this problem on my Android devices? I look at the preferences and didn't find such option there.