download - Firefox cannot save files (most of the time), how to solve? - Super User

this not full duplicate of this question or this question, though base question same. however, questions have no answers.

for on half year have problems downloading files firefox. when click on download link, download dialog opened asking me do, save or open it. immediately, there error/warning pop-up (twice, can see 1 @ first) ok button. looks this message :

"c:\users\%user%\appdata\local\temp\wbbdv9k8.zip.part not saved because source file not read.

try again later or contact server administrator."

replace '%user%' name of user trying download.

after closing pop-up, download dialog disappears , have minimize firefox , open again, see other pop-up.

downloading exact same file internet explorer work, not desired.

i tried solutions here.
tried solutions here.
tried disabling extensions.
tried fixing permissions on temp folder.
tried making files , folder in profile directory non-readonly.
tried running firefox administrator.
tried disabling firewall.
tried "save link as...".
tried selecting different downloads folder. (though clear not problem)
tried resetting firefox. (via about:support).
tried clearing setting "network.http.accept-encoding" in about:config.

the resetting seemed work @ first until tried update flash, first occurence of problem since reset , after few other downloads. problem updating flash cannot save file, because flash tries himself.

very though, downloading of file work , not receive error message. however, chance feels 1 in 100.

on moment of writing question using firefox 44.0, problem few versions old @ least. also, problem did not occur before when using same extensions.
in meanwhile upgraded windows 7 windows 10, problem still persists.

i able ignore warning , click on download dialog , click ok. puts download in corrupt state cannot cancel. way remove closing firefox.

current workaround:
after download failed, can go download library clicking on blue download icon. can click on retry icon , download succesfully finished. works however, when click on ok button of dialog , therewith dismissing download dialog.

i'm running out of options, more can try? possible disable 'predownloading' skipping temp folder , directly download downloads folder, starting when click on ok button on download dialog?

install firefox administrator - right click, run administrator.