What is the site? And did you verify those are png/jpg opens without problem?

http://admission.du.ac.in/pg2018/index.php/uploads/create this site and yes I checked all the image type and size but it doesn't help

The mimeTypes.rdf file was replaced by handlers.json as of Firefox 55. The profiles article describing how to open your profile folder is located here, instructions on (re)moving the handlers.json file can be found at the bottom of this article.

thanks okay so i deleted that file but the website still doesn't work with the uploads what should i do?

okay there' another problem firefox has forgot all my passwords for other websites

okay so i just checked again the file does not get deleted even after i refresh mozilla

I was afraid of that. Is your Firefox connection set up to use a proxy or a pac file? If so, what happens if you select No proxy? (See Connection settings in Firefox for more info.) Are JavaScript and cookies enabled, and are you sure Firefox isn’t permanently in Private Browsing mode? Note that this mode is similar to setting it to Never remember history.

i have changed to- no proxy cookies are being accepted from websites mozilla remembers my history handlers won't go

also, when i refresh firefox, it automatically changes from 'no proxy' to 'use system proxy settings'

(Please try to use the Edit this post link rather than posting new.)

Refreshing causes Firefox to use default settings, one of which being Use system proxy settings, so that’s fine, although you may want or even need to change it to No proxy or some other setting. Did you test for the issue at that point? The handlers.json file should remain too and not get deleted, to that’s fine too.

Firefox forgetting passwords however is more serious - this should not happen, unless you have set it to use Private browsing mode. Are you sure you didn’t select Never remember history? See Settings for privacy, browsing history and do-not-track for more on that.

You can also create a new profile, run Firefox with that, and test the behavior for uploads as well as remembering passwords. If that’s OK, consider recovering important data from an old profile.

okay sure but actually the main problem is that i still cannot upload the documents on that website because you said to delete handlers.json so i did but the website shows errors in uploading and thanks for the recovery part- i have checked privacy settings and it's not on private browsing mode

I understand. Please remember that you wanted to remove the file since it was offered as a solution for the other question. Removing the file may only be necessary if it’s corrupted in some way, then it should remain as is and left untouched. To be honest, I think it’s an odd solution, as it should only define how to handle downloaded files.

Please try to think along as well as suggested steps. Look at the other question and try opening the Browser Console (Ctrl+Shift+K) to find error messages. The add-on mentioned in that question unfortunately is no longer compatible with Firefox Quantum.

Do you have any reports from users able to upload file with Firefox on the university network anyway in order to verify? Does it work with other browsers? Did or can you contact the administrators for the issue?

hmm okay no i don't information of other users it does not work with chrome the administrator doesn't know a thing

but thanks for your time :) you really have put an effort in writing all that thank you