Sounds like you have the pdf reader extension installed 
No, PDF files are handled by Firefox 45.9.0 (and possibly earlier versions). In fact, FF handles them better than Lucide does (although I am not sure if they can be edited). AFAIK, I have no extensions installed. I have found no need for any of them.
Ivan's problem is in his profile
I think the main problem, is trying to use plugins, and add-ons. I don't use any of those things, and any that I have tried, do nothing but cause trouble.
As for his problems with 45.9, probably a library problem.
More likely an add-on, or plugin problem, unless he has tried to manually update the RPM/YUM stuff, which is pretty well guaranteed to cause problems.
I will note, that I used Ad-Block, and FLASH-block, at one time. I tried No-Scrpt too, but it never worked properly, for me. I abandoned them some time ago, simply because the HOSTS file from
http://winhelp2002.mvps.org/hosts.htm works just as well (READ the page), and doesn't cause problems in FF (you may need to add any entries that you need for your own use, after the localhost line, and before the rest). Just replace C:\MPTN\ETC\HOSTS with the one from the download.