The slowness means the CPU is being overworked.

Why are you using Firefox instead of a text program?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

https://support.mozilla.org/en-US/kb/websites-look-wrong-or-appear-differently

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

I work in support. We have a log repository on the server, accessed via browser. It simply opens text file in browser window and provides me with a quick look into log. It doesn't matter, if the file is loading from network or if the file is already loaded. It is still slow and almost unresponsive, when searching strings.

I started Firefox in SafeMode. I could see slightly better performance, but it is still almost unusable.

I have just tested it with IE and the result is the same. It looks it has something to do with Windows, rather than browser itself. Or perhaps it is related to our log repository server. I have no outside link for such large text files (>1MB) other then our server to test.

Have you compared what happens if you download the log file and then search it in Firefox. From your first post it sounds as if you have and find no difference.

I just tried loading a 1/2 MB plain text file & Firefox had no issues searching it in real time. Many search strings indicated over 100 matches but the matches kept up with my admittedly slow typing. I am using Windows at present. I did only test on a 1/2 MB file if necessary I could just copy and paste such chunks to concatenate into a much larger file, but from your second post it sounds like you are tending to rule out this issue being Firefox specific.

John99 said

Have you compared what happens if you download the log file and then search it in Firefox. From your first post it sounds as if you have and find no difference. I just tried loading a 1/2 MB plain text file & Firefox had no issues searching it in real time. Many search strings indicated over 100 matches but the matches kept up with my admittedly slow typing. I am using Windows at present. I did only test on a 1/2 MB file if necessary I could just copy and paste such chunks to concatenate into a much larger file, but from your second post it sounds like you are tending to rule out this issue being Firefox specific.

The searching itself can be fast, but the typing is the problem. First 1-3 letters appear quickly, but each next letter takes ages to appear (it seems it is searching the text for the 3rd...4th...letter, what takes terribly slow). And yes, it happens with both Firefox and IE.

The only workaround for me is to download text file to local HDD and open it in Notepad or any other text viewer/editor. It is annoying compared what Firefox was giving to me in that matter couple versions ago.

What is notable is your discovery IE & Firefox have the same issue. That almost certainly indicates it is a local or machine specific problem.

Do I understand you see a slow search in Firefox when that file is on the local hdd ? My test on a 1/2 MB text test file had no issues with searching for long words or multiple words. Are you able to try with a text file of about 1/2 MB on the hdd for comparison. What sort of size are your problem log files  ? I will create and test with a similar size file on my hdd. I have multiple versions of Firefox available which version worked I can compare that, although I suspect it may not make a difference . As a more realistic test if you wish to post a public test text file & give me the link I will test that.

If this is actually a regression between versions it would be fairly serious & probably be reported & fixed quickly.

John99 said

What is notable is your discovery IE & Firefox have the same issue. That almost certainly indicates it is a local or machine specific problem. Do I understand you see a slow search in Firefox when that file is on the local hdd ? My test on a 1/2 MB text test file had no issues with searching for long words or multiple words. Are you able to try with a text file of about 1/2 MB on the hdd for comparison. What sort of size are your problem log files  ? I will create and test with a similar size file on my hdd. I have multiple versions of Firefox available which version worked I can compare that, although I suspect it may not make a difference . As a more realistic test if you wish to post a public test text file & give me the link I will test that. If this is actually a regression between versions it would be fairly serious & probably be reported & fixed quickly.

Hello, you are right. This must be machine specific. I have tried to copy that file (>2MB) to my home computer and all is working smoothly, while my work laptop (newer model and reinstalled to W10) is still searching slow. Even when I open the file from local HDD (file:///C:). I can not share the file, bcs. it contains sensitive client's info. However, it happens with any larger text file (about 2MB of size).

Thanks for the reply, but it is no longer looking like a Firefox problem so there is not much I can do. It would be interesting to know in due course what the problem and solution is.