FF sometimes issues malformed requests (Accept-Language contains a line break) ==> error 400
A few days ago, I started getting 400 errors on some (not all) sites. I would get errors like
---snip--- Bad Request
Your browser sent a request that this server could not understand. Request header field is missing ':' separator.
- q=0.8,en-CA-x-rogers;q=0.8,en-IE;q=0.7,it-IT;q=0.7,it;q=0.6,es-ES;q=0.6,es;q=0.
---snip---
I discovered that FF was sending a malformed request -- notice how the Accept-language header is broken by a single newline. (I made /r and /n visible.)
---snip--- GET / HTTP/1.1\r\n Host: www.thestar.com\r\n User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0\r\n Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n Accept-Language: en-US,en,en-ca;q=0.9,en-gb;q=0.9,fr-FR;q=0.9,fr;q=0.8,fr-ca\n
- q=0.8,en-CA-x-rogers;q=0.8,en-IE;q=0.7,it-IT;q=0.7,it;q=0.6,es-ES;q=0.6,es;q=0.6,ko-KR;q=0.5,ko;q=0.5,is-IS;q=0.5,is;q=0.4,de-DE;q=0.4,de;q=0.4,cs-CZ;q=0.3,cs;q=0.3,ru-RU;q=0.3,ru;q=0.2,ca-AD;q=0.2,ca;q=0.1,en-AU;q=0.1,pl-PL;q=0.1,pl;q=0.0\r\n
Accept-Encoding: gzip, deflate\r\n Connection: keep-alive\r\n \r\n ---snip---
I tried the suggested steps: emptied the cache/cookies/active logins/offline website data, closed FF, deleted the cookies.sqlite file, restarted. The problem persists. The only clue is the malformed Accept-Language header.
Having a crippled FF is no fun. Thanks for your help.
Chosen solution
Do you really need all those languages?
Tools > Options > Content: Languages->Choose
Read this answer in context 👍 1All Replies (5)
Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.
You can try some of the following programs to scan for malware:
- MalwareBytes' Anti-Malware
- TDSSKiller - AntiRootkit Utility
- Microsoft Security Essentials (A good permanent anti-virus if you don't already have one)
Further information can be found in the Troubleshoot Firefox issues caused by malware article.
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Try the Firefox Safe Mode to see how it works there. The Safe Mode is a troubleshooting mode, which disables most add-ons.
(If you're not using it, switch to the Default theme.)
- You can open the Firefox 4.0+ Safe Mode by holding the Shift key when you use the Firefox desktop or Start menu shortcut.
- Or use the Help menu item and click on the Restart with Add-ons Disabled... menu item while Firefox is running.
Don't select anything right now, just use "'Start in Safe Mode" To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut (without the Shift key) to open it again. If it is good in the Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one.
Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.
When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.
This can be caused by corrupted cookies.
Clear the cache and the cookies from sites that cause problems.
"Clear the Cache":
- Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"
"Remove Cookies" from sites causing problems:
- Tools > Options > Privacy > Cookies: "Show Cookies"
It wasn't malware, or cookies, or anything else. Somehow, FF was using a malformed Accept-language setting.
- I opened a tab at about:config and filtered the settings on intl. .
- I saw that there was a small gap in the intl.accept_languages setting.
- I removed the gap to ensure the value was one continuous string. (en-US,en,en-ca,en-gb,fr-FR,fr,fr-ca,en-CA-x-rogers,en-IE,it-IT,it,es-ES,es,ko-KR,ko,is-IS,is,de-DE,de,cs-CZ,cs,ru-RU,ru,ca-AD,ca,en-AU,pl-PL,pl)
- The problem was instantly fixed.
Chosen Solution
Do you really need all those languages?
Tools > Options > Content: Languages->Choose
Good point! Thanks for prompting me to pare down my accepted languages.