Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues. Not really as have no needed information that would been sent. So all there is is guessing.

List your Extensions......

You mention went to get a extension but would not install. Never mention the name of the extension which is important.

You do not mention if you had problems installing any other extensions. This would be good information also.

You go from 1 browser to another with out a solution. You make changes but never mention if those changes were reverted when did not work.

So Uninstall Firefox, delete the Mozilla Firefox Folders in C;\Program Files and in C:\Program Files (X86) Reboot. Use Microsoft Disk Cleanup to cleanup temp files and such. Then run it again and Click Cleanup System Files.

Reinstall 56.0.2 https://www.mozilla.org/firefox/all/ Full Version Installer

Now stay there until you have provided answers to the above 4 missing information items, 3 actually.

Please let us know if this solved your issue or if need further assistance.

Pkshadow said

Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues. Not really as have no needed information that would been sent. So all there is is guessing. List your Extensions...... You mention went to get a extension but would not install. Never mention the name of the extension which is important. You do not mention if you had problems installing any other extensions. This would be good information also. You go from 1 browser to another with out a solution. You make changes but never mention if those changes were reverted when did not work. So Uninstall Firefox, delete the Mozilla Firefox Folders in C;\Program Files and in C:\Program Files (X86) Reboot. Use Microsoft Disk Cleanup to cleanup temp files and such. Then run it again and Click Cleanup System Files. Reinstall 56.0.2 https://www.mozilla.org/firefox/all/ Full Version Installer Now stay there until you have provided answers to the above 4 missing information items, 3 actually. Please let us know if this solved your issue or if need further assistance.

There I added some stuff if that helps,

I am running Windows 10 and it's not a specific add-on, it's all add-ons that are giving me this error. The extensions I previously had before this incident were; Honey Badger, Ublock Origin, Greasemonkey, and Reddit Enhanced Suite. When I noticed I couldn't get any add-ons to install, I tried doing research and read about reinstalling Firefox. So I renamed the Firefox folders in C:\Program Files and C:\Program Files (x86) becasue I didn't want to risk losing anything. Then I uninstalled FF 56, and reinstalled it only to have the same issue. So then I decided I could try Firefox 57 beta, but still the issue persists.

Here is an error I get when trying to install add-ons (Greasemonkey for this example)

1509981683138 addons.xpi DEBUG Download started for https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8 to file C:\Users\Chris\AppData\Local\Temp\tmp-nxf.xpi 1509981683146 addons.xpi DEBUG Download of https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8 completed. 1509981684384 addons.xpi DEBUG Starting install of {e4a8a97b-f2ed-450b-b12d-ee082ba24781} from https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8 1509981684423 addons.xpi ERROR Failed to create staging directory: Win error 5 during operation makeDir on file C:\Users\Chris\AppData\Roaming\Mozilla\Firefox\Profiles\2vz0dtxl.default-1509927298758\extensions\staged (Access is denied.

) ((unknown module)) No traceback available Log.jsm:752 1509981684424 addons.xpi WARN Failed to install C:\Users\Chris\AppData\Local\Temp\tmp-nxf.xpi from https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8 to C:\Users\Chris\AppData\Roaming\Mozilla\Firefox\Profiles\2vz0dtxl.default-1509927298758\extensions\staged: Win error 5 during operation makeDir on file C:\Users\Chris\AppData\Roaming\Mozilla\Firefox\Profiles\2vz0dtxl.default-1509927298758\extensions\staged (Access is denied.

) ((unknown module)) No traceback available 1509981684436 addons.xpi DEBUG removeTemporaryFile: https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8 removing temp file C:\Users\Chris\AppData\Local\Temp\tmp-nxf.xpi 1509981684436 addons.xpi WARN Failed to remove temporary file C:\Users\Chris\AppData\Local\Temp\tmp-nxf.xpi for addon https://addons.cdn.mozilla.net/user-media/addons/748/greasemonkey-4.0-an+fx-windows.xpi?filehash=sha256%3A27f9e7a142b2b4a1dc2a2d4f8d7170d3009a01189bb20a3d1e39c46141c3a8e8: [Exception... "Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFile.remove]" nsresult: "0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: removeTemporaryFile :: line 1558" data: no] Stack trace: removeTemporaryFile()@resource://gre/modules/addons/XPIInstall.jsm:1558 < startInstall/<()@resource://gre/modules/addons/XPIInstall.jsm:1907

Bump?

UserUnavailable404 said

Bump?

Yes none of those are going to work. If you just need a few then : This seems to work well if there is a Firefox 57 compatible Extension. Can use google search terms : Firefox Extension <old extension name> Comparable Note : that should go to each Developers Web Page and look around and go there support pages. Some Developers are still coding.

Your Profile is not in any of those Folders you renamed. https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

So to do a proper uninstall you do uninstall then delete those folders.

Now there is ways to go back to previous but there is a lot to it and do not yet know it. You can go straight to 52,4,1 ESR Version that gets security updates. This would be a good fix until find other Extensions that are comparable to Version 57. https://www.mozilla.org/en-US/firefox/organizations/all/

This is what I give for uninstalling : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved.

As said to be safe save your profile, screen shoot your passwords and go to Bookmarks --> Show all Bookmarks --> Import & Export --> save as HTML (still have mine since Win95)

Please let us know if this solved your issue or if need further assistance.