Even in some case scrolling back to the top makes you lose the progress. And that happens automatically when you do a Ctr-F and start typing, the matching of the first character you type will likely be at the top of the page.
Which may now be obsolete. Over the last year firefox has implemented some amazing flexbox layout computation improvements that make appending to a flexbox with many elements (>5k) stay fast. It only re-computes the changed ones.
Of course you need to do some profiling to check that you don't accidentally deviate from the happy path by introducing changes that touch all elements.
I noticed when trying to screenshot a Twitter thread in Firefox that twitter does this, on the mobile site at least.