I have a Nexus 6 updated with the latest OS version and FF. I spend about 90% of my browsing time on HN, LinkedIn, and a couple of miscellaneous other news sites. I observe the following problems:
Loss of UI, where the only thing I see is either a white or black screen. Swiping up or down as if to scroll or refresh "peels back" some of this to reveal the web page underneath, but it doesn't become functional unless I end the app. This affects all tabs open.
Terrible latency acting on navigation, where I'll press a link which has clearly been detected (an outline appears around it) and...nothing happens for seconds. Doesn't matter if I have one tab or a dozen open.
Terrible detection of which link was pressed. Sometimes it's bad enough that a link more than halfway down the page from where I touch is activated. This doesn't happen in any other app I have, even when it's happening on FF.
Poor download times. The bar indicating progress will occasionally stop at about 80% and pause. Sometimes when it pauses it finishes after a few seconds and other times it simply freezes.
I Have the same phone but don't recognize these issues. I've seen something similar to the blank page thing but it sorts itself out without restarting the app.
I notice you specifically mention LinkedIn. I don't use that site but I did read their recent web development blog post when they admitted that they had a CSS download of 3.5MB that was causing issues for mobile users. Apparently they've fixed that now, would be interesting to see if that was a cause.
Definitely not my experience but I believe you. If FF runs so bad on some phones Mozilla has still a lot of work to do. Maybe they should start with a list of phones that are known to run FF well (eg. Sony Xperia Compact) and badly (which phone do you have?) and start digging into what's wrong with ones in the latter list.
I'm on a Note 3 (great phone, 5 years old) with a Snapdragon 800 vs your Snapdragon 805. Seems we both have 3GB RAM.
I do notice that links in FF are harder to hit accurately compared to Chromium - am guessing Chromium increases the hit area on buttons or uses some intelligence to look for the button closest to a touch... because it seems like it's just being forgiving on my sloppy touches (as opposed to FF being inaccurate). Admittedly a better UX in that respect regardless.
Otherwise I don't have any of these issues, FF is completely smooth for me. I wonder if you have some other software causing a problem, maybe FF add-ons?
(EDIT: I'm also on LineageOS 14.1 which is based on Nougat so maybe the sibling comment about Oreo is onto something)
Loss of UI, where the only thing I see is either a white or black screen. Swiping up or down as if to scroll or refresh "peels back" some of this to reveal the web page underneath, but it doesn't become functional unless I end the app. This affects all tabs open.
Terrible latency acting on navigation, where I'll press a link which has clearly been detected (an outline appears around it) and...nothing happens for seconds. Doesn't matter if I have one tab or a dozen open.
Terrible detection of which link was pressed. Sometimes it's bad enough that a link more than halfway down the page from where I touch is activated. This doesn't happen in any other app I have, even when it's happening on FF.
Poor download times. The bar indicating progress will occasionally stop at about 80% and pause. Sometimes when it pauses it finishes after a few seconds and other times it simply freezes.