I was try to open a pdf file instead of dled it but I pressed the wrong button

I'm using firefox for android on an asus tablet. I was trying to view online a pdf file but pressed the wrong choice and now instead of viewing the file with the drive viewer, the pdf is always downloaded. I tried to change the default setting in the app manager but in the firefox app there was no default set and even trying to return to the set default from the menu in the app manager changed nothing. How can I return to the box choice of always and just now? Sorry but I'm not first language english

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