Works for me on Linux.

Can you drag a file in a Firefox window or to free area (or the newtab +) on the Tab bar? Does this happen with all file types (.txt , .html)?

Accessing any file via a web server ( http://..... ) works as normal, however attempting to open ANY local file (e.g. /temp/testfile.html, file://temp/testfile.html, etc) and any file type (html, pdf, jpg, etc) using ANY method (drag-drop, using "file open" menu item, entering full file path into the url bar, etc only opens an EMPTY tab. No error messages displayed, in fact nothing to indicate what the problem is.

Opening the same files using other browsers works OK.

This same problem appeared a few releases ago (sorry, can't remember which version), then went away following another firefox update a few days later.

Could be a sandbox issue related to multi-process.

• try to set security.sandbox.content.level = 0 on the about:config page
• try to disable multi-process windows in Firefox to see if that has effect

You can disable multi-process windows in Firefox by setting these prefs to false on the about:config page.

• browser.tabs.remote.autostart = false
• browser.tabs.remote.autostart.2 = false

• http://www.ghacks.net/2016/07/22/multi-process-firefox/

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

Similar reports (unsolved):

• https://support.mozilla.org/questions/1157104
• https://support.mozilla.org/questions/1157573

There is NO "security.sandbox.content.level" (or anything even remotely similar) in about:config!

browser.tabs.remote.autostart was set to false browser.tabs.remote.autostart.2 WAS true, but setting it to false makes no difference at all.

about:support shows multiprocess windows as disabled.

This appears to be the same problem as the "unsolved" report mentioned by jscher2000 (https://support.mozilla.org/questions/1157104).

Is there any difference if you try to open the files in Firefox's Safe Mode? In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement? (More info: Diagnose Firefox issues using Troubleshoot Mode)

In safe mode I can open local files. Turning safe mode off results in being unable to open local files again.

I then followed the suggestions in the "troubleshooting firefox issues using safe mode" link. I then disabled the noscript 5.0.3 add-on - I can now open local files.

So it appears that noscript doesn't like firefox 53.0.....

Mick.

Hmm, I'm running NoScript myself and haven't had this problem...

When I look at the NoScript forum, there is a thread about this: https://forums.informaction.com/viewtopic.php?f=7&t=22761

The consensus there is if you turned on "Allow local links" for Trusted sites, then file:/// doesn't load. You can turn that off here:

NoScript "S" button > Options > Advanced > Trusted mini-tab

See attached screenshot

Or:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste nosc and pause while the list is filtered

(3) If the noscript.allowLocalLinks preference is bolded and "user set" to true, double-click it to restore the default value of false

noscript.allowLocalLinks was set to true, so I've reset it to false.

Local files now working again with NoScript re-enabled!  :-)

Thanks for the help!