Why are most websites only displaying code like text?

Question

Almost all of the web sites that I frequent have began displaying code like text on a blank white background. Some sites still have hyperlinks and images here and there with random text, but others are fully blank with what appears to be the code of the website showing. I wasn't able to access this web site until I tried multiple times and it magically worked, but others are still not working. The only sites that I have tested that have worked from the start are Google related sites (Gmail, Google, Youtube). My yahoo email is inaccessible, which is an important email for me and all other sites that i frequent are inaccessible. One major thing to note is that the sites are also inaccessible on Internet Explorer. This would typically lead you to believe that the problem lies with your connection in some way. I have reset my router/modem and it had no effect. I also have ran CCleaner and have deleted temp files, cookies, and caches. I have tried running Mozilla in safe mode with add-ons disabled as well. My malware protection and antivirus protection find no issues after completing full scans. One last thing to note is that, on both Firefox and IE, certain sites allow to me to access the homepage, such as yahoo, but once I attempt to check my mail the random display of code appears. On IE it simply says that the site cannot be displayed once I click to check my mail. Gmail works perfect on the other hand. The only things that I have done during this time are:
Setup a LogMeIn account (Hamachi) and connected my PC to their service
Downloaded and began using Malewarebytes software to remove malware that I had picked up
Other than those two things it has been the same usual actions on my PC. Could the malware that I had still be effecting me somehow even though it was found/deleted? Is my router to blame even though resetting it does not help? After all the things I have tried, what could it be?

Answer 1

What is the content type of those pages if you check that via Tools > Page Info > General?
Is that text/html as it should be or text/plain as your screenshot would suggest?
You can also check the Net log via the Web Console (Web Developer > Web Console;Ctrl+Shift+K)
*https://developer.mozilla.org/en/Tools/Web_Console
*https://developer.mozilla.org/en/Using_the_Web_Console
This can be a problem with your firewall that modifies the server response headers if the settings in Firefox are correct.
*http://kb.mozillazine.org/Standard_diagnostic_-_Firefox
*https://support.mozilla.org/kb/Basic+Troubleshooting
A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.
Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.
See:
*https://support.mozilla.org/kb/Server+not+found
*https://support.mozilla.org/kb/Firewalls
Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that works.